The introduction and utilization of new maize (Zea mays L.) germplasm from sources, such as the International Maize and Wheat Improvement Center (CIMMYT), can be valuable for broadening the genetic base of breeding populations through the introgression of new alleles. Twenty‐five inbred lines, derived from CIMMYT breeding populations, were selected on the basis of grain color, resistance to turcicum leaf blight, and per se line performance in Yunnan. To use the lines effectively, information on their performance in hybrid combinations and on general combining ability (GCA) and specific combining ability (SCA) needed to be obtained. The objectives of this study were (i) to evaluate these lines for grain yield (GY) in hybrid combinations and determine GCA of parental lines and SCA of crosses between the 25 introduced lines and six testers using North Carolina Design II; and (ii) to classify the lines into different maize heterotic groups. The field testing at three locations identified crosses with lines from Cateto and Population 147 (P147) as having significantly higher GY than those from SA3 and other introduced populations, and the high GY was largely attributable to their high positive GCA effects. Lines from the same population were not necessarily classified into same maize heterotic group. Lines selected at S4 or a later generation would be expected to have more stable GCA effects than lines selected in earlier generations.

Genetic variabiltiy is essential for continued genetic improvement of any crop species. One potential sourse of genetic variability is the use of exotic or unadapted germplasm. Although considerable genetic variability may be available in germplasm repositories, indiscriminate introduction of exotic germplasm may lower the breeding value of elite, adapted populations. Exotic germplasm that has been improved by cyclical selection should reduce some of the detrimental effects of incorporating exotic sources into adapted sources. The objective of our study was to determine the relative yields of maize (Zea mays L.) populations developed by recurrent selection in Mexico and in the United States. Trials were conducted in each country to determine the response of the populations per se and their population crosses. The U.S. Corn Belt populations performed better in Mexico than did the Mexican populations in the U.S. Corn Belt and some of the Mexican by U.S. Corn Belt population crosses tested in Mexico did not differ from the check hybrid. The U.S. Corn Belt populations showed better adaptation to Mexican environments than the Mexican populations did to U.S. Corn Belt environments. Of the populations tested, BS13(S)C2, derived from ‘Stiff Stalk Synthetic’ after nine cycles of recurrent selection for yield, had the highest general combining ability with the improved Mexican populations. Thus, it appeared that U.S. Corn Belt populations could be sources of useful alleles for yield, earlier maturity, and shorter plant height for Mexican breeding programs located in tropical and subtropical areas. None of the Mexican populations per se or their crosses approached the yield of the check hybrid when tested in the U.S. Corn Belt; most were taller, flowered later, and had higher grain moisture at harvest.

Use of photoperiod‐sensitive tropical germplasm for breeding in temperate regions is hampered by several problems. The inability to accurately evaluate photoperiodically sensitive accessions under long‐day conditions leads to an inability to choose the best available materials. The use of short‐day seasons in Homestead, FL, and Weslaco, TX has been investigated for the screening of the available set of typical accessions of the Latin American maize (Zea mays L.) races. Nursery data were used to select about 400 better accessions from a set of some 1300 typical accessions. Replicated trials under short‐day conditions, which for maize act as day‐neutral conditions, were used to screen the selected accessions, with temperate and tropical hybrids used as standards for comparison. Yield distributions of the tropical accessions were symmetric under short‐day conditions (in Florida and Texas), but highly skewed toward zero under longday conditions (in North Carolina) for all but the earliest maturity group. When yields and differences in male and female flowering times were plotted against latitude, distinctly different patterns were observed under long‐ and short‐day conditions. Under long‐day conditions, yields were greatly depressed, and differences between male and female flowering greatly increased for accessions originally collected between 15 °C N and 15 °C S latitude, as compared to results under short‐day conditions, where both yields and male vs. female flowering differences had largely linear regressions on latitude, with slopes near zero. Under short‐day test conditions, it was possible to identify races of maize and specific geographic regions as promising sources of tropical maize germplasm for temperate breeding programs.

Maize (Zea mays) originated in southern Mexico and has spread over a wide latitudinal range. Maize expansion from tropical to temperate regions has necessitated a reduction of its photoperiod sensitivity. In this study, we cloned a quantitative trait locus (QTL) regulating flowering time in maize and show that the maize ortholog of Arabidopsis thaliana EARLY FLOWERING3, ZmELF3.1, is the causal locus. We demonstrate that ZmELF3.1 and ZmELF3.2 proteins can physically interact with ZmELF4.1/4.2 and ZmLUX1/2, to form evening complex(es; ECs) in the maize circadian clock. Loss-of-function mutants for ZmELF3.1/3.2 and ZmLUX1/2 exhibited delayed flowering under long-day and short-day conditions. We show that EC directly represses the expression of several flowering suppressor genes, such as the CONSTANS, CONSTANS-LIKE, TOC1 (CCT) genes ZmCCT9 and ZmCCT10, ZmCONSTANS-LIKE 3, and the PSEUDORESPONSE REGULATOR (PRR) genes ZmPRR37a and ZmPRR73, thus alleviating their inhibition, allowing florigen gene expression and promoting flowering. Further, we identify two closely linked retrotransposons located in the ZmELF3.1 promoter that regulate the expression levels of ZmELF3.1 and may have been positively selected during postdomestication spread of maize from tropical to temperate regions during the pre-Columbian era. These findings provide insights into circadian clock-mediated regulation of photoperiodic flowering in maize and new targets of genetic improvement for breeding.

Maize was originally domesticated in a tropical environment but is now widely cultivated at temperate latitudes. Temperate and tropical maize populations have diverged both genotypically and phenotypically. Tropical maize lines grown in temperate environments usually exhibit delayed flowering, pollination, and seed set, which reduces their grain yield relative to temperate adapted maize lines. One potential mechanism by which temperate maize may have adapted to a new environment is novel transposable element insertions, which can influence gene regulation. Recent advances in sequencing technology have made it possible to study variation in transposon content and insertion location in large sets of maize lines.In total, 274,408 non-redundant TEs (NRTEs) were identified using resequencing data generated from 83 maize inbred lines. The locations of DNA TEs and copia-superfamily retrotransposons showed significant positive correlations with gene density and genetic recombination rates, whereas gypsy-superfamily retrotransposons showed a negative correlation with these two parameters. Compared to tropical maize, temperate maize had fewer unique NRTEs but higher insertion frequency, lower background recombination rates, and higher linkage disequilibrium, with more NRTEs close to flowering and stress-related genes in the genome. Association mapping demonstrated that the presence/absence of 48 NRTEs was associated with flowering time and that expression of neighboring genes differed between haplotypes where a NRTE was present or absent.This study suggests that NRTEs may have played an important role in creating the variation in gene regulation that enabled the rapid adaptation of maize to diverse environments.

Plants are highly sensitive to temperature, and climate change is predicted to have negative impacts on agricultural productivity. Warming temperatures, coupled with a growing population, present a substantial challenge for food security and motivate research to understand how plants sense and respond to changes in temperature. Here, we synthesize our current understanding of temperature sensing and response in plants. We outline how temperature cues are integrated into preexisting signaling cascades using inherently temperature-sensitive proteins or processes. This dispersed nature of thermo-sensitive proteins and processes makes distinct signaling cascades sensitive to temperature. This model integrates current knowledge and distinguishes thermosensing from other conventional sensing and signaling mechanisms in plants.

Maize (Zea mays L.) is a typical short-day plant that is produced as an important food product and industrial material. The photoperiod is one of the most important evolutionary mechanisms enabling the adaptation of plant developmental phases to changes in climate conditions. There are differences in the photoperiod sensitivity of maize inbred lines from tropical to temperate regions. In this study, to identify the maize proteins responsive to a long photoperiod (LP), the photoperiod-insensitive inbred line HZ4 and its near-isogenic line H496, which is sensitive to LP conditions, were analyzed under long-day conditions using isobaric tags for relative and absolute quantitation. We identified 5259 proteins in maize leaves exposed to the LP condition between the vegetative and reproductive stages. These proteins included 579 and 576 differentially accumulated proteins in H496 and HZ4 leaves, respectively. The differentially accumulated proteins (e.g., membrane, defense, and energy- and ribosome-related proteins) exhibited the opposite trends in HZ4 and H496 plants during the transition from the vegetative stage to the reproductive stage. These results suggest that the photoperiod-associated fragment in H496 plants considerably influences various proteins to respond to the photoperiod sensitivity. Overall, our data provide new insights into the effects of long-day treatments on the maize proteome, and may be useful for the development of new germplasm.

\n Accelerator mass spectrometry age determinations of maize cobs\n (\n Zea mays\n L.) from Guilá Naquitz Cave in Oaxaca,\n Mexico, produced dates of 5,400 carbon-14 years before the present\n (about 6,250 calendar years ago), making those cobs the oldest in the\n Americas. Macrofossils and phytoliths characteristic of wild and\n domesticated\n Zea\n fruits are absent from older strata\n from the site, although\n Zea\n pollen has previously been\n identified from those levels. These results, together with the modern\n geographical distribution of wild\n Zea mays,\n suggest that\n the cultural practices that led to\n Zea\n domestication\n probably occurred elsewhere in Mexico. Guilá Naquitz Cave has now\n yielded the earliest macrofossil evidence for the domestication of two\n major American crop plants, squash (\n Cucurbita pepo\n ) and\n maize.\n

\n Mexico is recognized as the center of origin and domestication of maize. Introduction of modern maize varieties (MVs) into Mexico raised concerns regarding the possible effects of gene flow from MVs into maize landraces (LRs) and their wild relatives (WRs), teosintes. However, after more than 60 y from the release of the first MVs, the impact of the sympatry with LRs and their WRs has not been explored with genetic data. In this work, we assessed changes in the genomes of 7 maize LRs and 2 WR subspecies from collections spanning over 70 y. We compared the genotypes obtained by genotyping by sequencing (GBS) for LRs and WRs before and after the adoption of MVs, and observed introgression from sympatric MVs into LRs and into the WR\n Zea mays\n ssp.\n mexicana\n sampled after the year 2000. We also found a decrease in the paired divergence index (\n F\n \n ST\n \n ) between MV-LR and MV-WR over the same time frame. Moreover, we determined that LR genetic diversity increased after 2000, probably as a result of gene flow from MVs introduced in the 1990s. Our findings allowed us to identify ongoing changes in the domesticated and wild maize genetic pools, and concur with previous works that have evaluated short-term gene flow from MVs into LRs in other crops. Our approach represents a useful tool for tracking evolutionary change in wild and domesticated genetic resources, as well as for developing strategies for their conservation.\n

By 4000 years ago, people had introduced maize to the southwestern United States; full agriculture was established quickly in the lowland deserts but delayed in the temperate highlands for 2000 years. We test if the earliest upland maize was adapted for early flowering, a characteristic of modern temperate maize. We sequenced fifteen 1900-year-old maize cobs from Turkey Pen Shelter in the temperate Southwest. Indirectly validated genomic models predicted that Turkey Pen maize was marginally adapted with respect to flowering, as well as short, tillering, and segregating for yellow kernel color. Temperate adaptation drove modern population differentiation and was selected in situ from ancient standing variation. Validated prediction of polygenic traits improves our understanding of ancient phenotypes and the dynamics of environmental adaptation.Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Diverse heterotic groups have been developed in China over several decades, but their genomic divergences have not been systematically studied after improvement. In this study, we performed Maize6H-60K array of 5,822 maize accessions and whole-genome re-sequencing of 150 inbred lines collected in China. Using multiple population structure analysis methods, we established a genetic boundary used to categorize heterotic groups and germplasm resources. We identified three chloroplast–cytoplasmic types that evolved during adaptation to diverse climatic environments in maize through phylogenetic and haplotype analyses. Comparative analyses revealed obvious genetic differences between heterotic groups and germplasm resources at both the chloroplast and nuclear genome levels, especially in the unique heterotic groups HG1 and HG2, which exhibited distinct regionality and genetic uniqueness. The divergent differentiation of heterotic groups from germplasm resources was driven by differential selection in specific genomic regions. Genome-wide selective sweep analysis identified core selected regions and candidate selected genes associated with traits between heterotic groups, highlighting that stress response- and plant defense-related genes were selected for environmental adaptation across a broad latitudinal range in China. Meanwhile, a genome-wide association study analysis provided evidence that core selected genes served as an important candidate gene pool with a potential role in genetic improvement. Gene exchanges among heterotic groups, which avoided the predominant heterotic patterns as much as possible, occurred to achieve population improvement during modern maize breeding. This study provides insights into the population differentiation and genetic characteristics of heterotic groups, which will facilitate the utilization of germplasm resources, the creation of novel maize germplasm, and the optimization of heterotic patterns during future maize breeding in China.

Increased planting densities have boosted maize yields. Upright plant architecture facilitates dense planting. Here, we cloned () and, two quantitative trait loci conferring upright plant architecture. is controlled by a two-base sequence polymorphism regulating the expression of a B3-domain transcription factor () located 9.5 kilobases downstream. exhibits differential binding by DRL1 (DROOPING LEAF1), and DRL1 physically interacts with LG1 (LIGULELESS1) and represses LG1 activation of regulates (), which underlies, altering endogenous brassinosteroid content and leaf angle. The allele that reduces leaf angle originated from teosinte, the wild ancestor of maize, and has been lost during maize domestication. Introgressing the wild allele into modern hybrids and editing enhance high-density maize yields.Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

Two quantitative trait loci (QTL) controlling differences in plant and inflorescence architecture between maize and its progenitor (teosinte) were analyzed. Complementation tests indicate that one of these, which is on chromosome arm 1L, is the locus for the maize mutant teosinte branched1 (tb1). This QTL has effects on inflorescence sex and the number and length of internodes in the lateral branches and inflorescences. This QTL has strong phenotypic effects in teosinte background but reduced effects in maize background. The second QTL, which is on chromosome arm 3L, affects the same traits as the QTL on 1L. We identify two candidate loci for this QTL. The effects of this QTL on several traits are reduced in both maize and teosinte background as compared to a maize-teosinte F2 population. Genetic background appears to affect gene action for both QTL. Analysis of a population in which both QTL were segregating revealed that they interact epistatically. Together, these two QTL substantially transform both plant and inflorescence architecture. We propose that tb1 is involved in the plant's response to local environment to produce either long or short branches and that maize evolution involved a change at this locus to produce short branches under all environments.

Teosinte, the probable progenitor of maize, has kernels that are encased in hardened fruitcases, which interfere with the use of the kernels as food. Although the components of the fruitcase are present in maize, their development is disrupted so that the kernels are not encased as in teosinte but exposed on the ear. The change from encased to exposed kernels represents a key step in maize evolution. The locus that largely controls this morphological difference between maize and teosinte, teosinte glume architecture 1, is described and genetically mapped.

Modern maize was domesticated from Zea mays parviglumis, a teosinte, about 9000 years ago in Mexico. Genes thought to have been selected upon during the domestication of crops are commonly known as domestication loci. The ramosa1 (ra1) gene encodes a putative transcription factor that controls branching architecture in the maize tassel and ear. Previous work demonstrated reduced nucleotide diversity in a segment of the ra1 gene in a survey of modern maize inbreds, indicating that positive selection occurred at some point in time since maize diverged from its common ancestor with the sister species Tripsacum dactyloides and prompting the hypothesis that ra1 may be a domestication gene. To investigate this hypothesis, we examined ear phenotypes resulting from minor changes in ra1 activity and sampled nucleotide diversity of ra1 across the phylogenetic spectrum between tripsacum and maize, including a broad panel of teosintes and unimproved maize landraces. Weak mutant alleles of ra1 showed subtle effects in the ear, including crooked rows of kernels due to the occasional formation of extra spikelets, correlating a plausible, selected trait with subtle variations in gene activity. Nucleotide diversity was significantly reduced for maize landraces but not for teosintes, and statistical tests implied directional selection on ra1 consistent with the hypothesis that ra1 is a domestication locus. In maize landraces, a noncoding 3'-segment contained almost no genetic diversity and 5'-flanking diversity was greatly reduced, suggesting that a regulatory element may have been a target of selection.

\n Domesticated maize and its wild ancestor (teosinte) differ strikingly in morphology and afford an opportunity to examine the connection between strong selection and diversity in a major crop species. The\n tb1\n gene largely controls the increase in apical dominance in maize relative to teosinte, and a region of the\n tb1\n locus 5′ to the transcript sequence was a target of selection during maize domestication. To better characterize the impact of selection at a major “domestication” locus, we have sequenced the upstream\n tb1\n genomic region and systematically sampled nucleotide diversity for sites located as far as 163 kb upstream to\n tb1\n. Our analyses define a selective sweep of ≈60–90 kb 5′ to the\n tb1\n transcribed sequence. The selected region harbors a mixture of unique sequences and large repetitive elements, but it contains no predicted genes. Diversity at the nearest 5′ gene to\n tb1\n is typical of that for neutral maize loci, indicating that selection at\n tb1\n has had a minimal impact on the surrounding chromosomal region. Our data also show low intergenic linkage disequilibrium in the region and suggest that selection has had a minor role in shaping the pattern of linkage disequilibrium that is observed. Finally, our data raise the possibility that maize-like\n tb1\n haplotypes are present in extant teosinte populations, and our findings also suggest a model of\n tb1\n gene regulation that differs from traditional views of how plant gene expression is controlled.\n

The characterization of genetic diversity and population differentiation for maize inbred lines from breeding programs is of great value in assisting breeders in maintaining and potentially increasing the rate of genetic gain. In our study, we characterized a set of 187 tropical maize inbred lines from the public breeding program of the Universidade Federal de Viçosa (UFV) in Brazil based on 18 agronomic traits and 3,083 single nucleotide polymorphisms (SNP) markers to evaluate whether this set of inbred lines represents a panel of tropical maize inbred lines for association mapping analysis and investigate the population structure and patterns of relationships among the inbred lines from UFV for better exploitation in our maize breeding program.Our results showed that there was large phenotypic and genotypic variation in the set of tropical maize inbred lines from the UFV maize breeding program. We also found high genetic diversity (GD = 0.34) and low pairwise kinship coefficients among the maize inbred lines (only approximately 4.00 % of the pairwise relative kinship was above 0.50) in the set of inbred lines. The LD decay distance over all ten chromosomes in the entire set of maize lines with r = 0.1 was 276,237 kb. Concerning the population structure, our results from the model-based STRUCTURE and principal component analysis methods distinguished the inbred lines into three subpopulations, with high consistency maintained between both results. Additionally, the clustering analysis based on phenotypic and molecular data grouped the inbred lines into 14 and 22 genetic divergence clusters, respectively.Our results indicate that the set of tropical maize inbred lines from UFV maize breeding programs can comprise a panel of tropical maize inbred lines suitable for a genome-wide association study to dissect the variation of complex quantitative traits in maize, mainly in tropical environments. In addition, our results will be very useful for assisting us in the assignment of heterotic groups and the selection of the best parental combinations for new breeding crosses, mapping populations, mapping synthetic populations, guiding crosses that target highly heterotic and yielding hybrids, and predicting untested hybrids in the public breeding program UFV.© 2021. The Author(s).

Despite the significant contributions of utilizing heterosis to crop productivity worldwide, the biological mechanisms of heterosis remained largely uncharacterized. In this study, we analyzed gene expression profiles of an elite rice hybrid and the parents at three stages of young panicle development, using a cDNA microarray consisting of 9198 expressed sequence tags (ESTs), with the objective to reveal patterns of gene expression that may be associated with heterosis in yield. A total of 8422 sequences showed hybridization signals in all three genotypes in at least one stage and 5771 sequences produced detectable signals in all slides. Significant differences in expression level were detected for 438 sequences among the three genotypes in at least one of the three stages, as determined by ANOVA validated with 100 permutations at P < 0.05. Significant mid-parent heterosis was detected for 141 sequences, which demonstrated the following features: a much larger number of sequences showed negative heterosis than ones showing positive heterosis; genes functioning in DNA replication and repair tended to show positive heterosis; genes functioning in carbohydrate metabolism, lipid metabolism, energy metabolism, translation, protein degradation, and cellular information processing showed negative heterosis; both positive and negative heterosis were observed for genes in amino acid metabolism, transcription, signal transduction, plant defense and transportation. The results are indicative of the biochemical and physiological activities taking place in the hybrid relative to the parents. Identification of genes showing expression polymorphisms among different genotypes and heterotic expression in the hybrid may provide new avenues for exploring the biological mechanisms underlying heterosis.

Understanding combining ability and heterosis among diverse maize germplasm resources is important for breeding hybrid maize ( L.). Using 28 temperate and 23 tropical maize inbreds that represent different ecotypes and worldwide diversity of maize germplasm, we first developed a large-scale multiple-hybrid population (MHP) with 724 hybrids, which could be divided into three subsets, 325 temperate diallel hybrids and 136 tropical diallel hybrids generated in Griffing IV, and 263 temperate by tropical hybrids generated in NCD II. All the parental lines and hybrids were evaluated for 11 traits in replicated tests across two locations and three years. Several widely used inbreds showed strong general combining ability (GCA), and their derived hybrids showed strong specific combining ability (SCA). Heterosis is a quantifiable, trait-dependent and environment-specific phenotype, and the response of parental lines and their hybrids to environments resulted in various levels of heterosis. For all the tested traits except plant height and hundred grain weight (HGW), NCD II (temperate × tropical) hybrids showed higher average heterosis than the temperate and tropical diallel hybrids, with higher hybrid performance for ear length, ear diameter, and HGW. Tropical maize germplasm can be used to improve the yield potential for temperate lines. Grain number per row and grain number per ear were two most important traits that determined yield heterosis, which can be used as direct selection criteria for yield heterosis. The hybrids from heterotic groups, Reid × SPT, Reid × LRC, SPT × PA, and Lancaster × LRC, contributed highly significant positive SCA effects and strong heterosis to yield-related traits, and the heterotic patterns identified in this study were potentially useful for commercial maize breeding. Heterosis was more significantly and positively correlated with SCA than GCA, indicating that SCA can be used in heterosis prediction to develop potential hybrids in commercial maize breeding. The results of the present study not only contribute to developing breeding strategies, but also improve targeted breeding efficiency by using both temperate and tropical maize to broaden genetic basis. Large sets of parental lines with available genotypic information can be shared and used in worldwide hybrid breeding programs through an open-source breeding strategy. Potential applications of the reported results in developing hybrid maize breeding strategies were also discussed.Copyright © 2020 Yu, Wang, Liu, Xu, Li, Xu, Liu, Wang and Xu.

In the context of climate change, drought is one of the most limiting factors that influence crop production. Maize, as a major crop, is highly vulnerable to water deficit, which causes significant yield loss. Thus, identification and utilization of drought-resistant germplasm are crucial for the genetic improvement of the trait. Here we report on a high-quality genome assembly of a prominent drought-resistant genotype, CIMBL55. Genomic and genetic variation analyses revealed that 65 favorable alleles of 108 previously identified drought-resistant candidate genes were found in CIMBL55, which may constitute the genetic basis for its excellent drought resistance. Notably, ZmRtn16, encoding a reticulon-like protein, was found to contribute to drought resistance by facilitating the vacuole H-ATPase activity, which highlights the role of vacuole proton pumps in maize drought resistance. The assembled CIMBL55 genome provided a basis for genetic dissection and improvement of plant drought resistance, in support of global food security.© 2023. The Author(s), under exclusive licence to Springer Nature America, Inc.

Hi-C is a popular technique to map three-dimensional chromosome conformation. In principle, Hi-C’s resolution is only limited by the size of restriction fragments. However, insufficient sequencing depth forces researchers to artificially reduce the resolution of Hi-C matrices at a loss of biological interpretability. We present the Hi-C Interaction Frequency Inference (HIFI) algorithms that accurately estimate restriction-fragment resolution Hi-C matrices by exploiting dependencies between neighboring fragments. Cross-validation experiments and comparisons to 5C data and known regulatory interactions demonstrate HIFI’s superiority to existing approaches. In addition, HIFI’s restriction-fragment resolution reveals a new role for active regulatory regions in structuring topologically associating domains.

Drought represents a major constraint on maize production worldwide. Understanding the genetic basis for natural variation in drought tolerance of maize may facilitate efforts to improve this trait in cultivated germplasm. Here, using a genome-wide association study, we show that a miniature inverted-repeat transposable element (MITE) inserted in the promoter of a NAC gene (ZmNAC111) is significantly associated with natural variation in maize drought tolerance. The 82-bp MITE represses ZmNAC111 expression via RNA-directed DNA methylation and H3K9 dimethylation when heterologously expressed in Arabidopsis. Increasing ZmNAC111 expression in transgenic maize enhances drought tolerance at the seedling stage, improves water-use efficiency and induces upregulation of drought-responsive genes under water stress. The MITE insertion in the ZmNAC111 promoter appears to have occurred after maize domestication and spread among temperate germplasm. The identification of this MITE insertion provides insight into the genetic basis for natural variation in maize drought tolerance.

利用RAPD分子标记技术，对我国目前25个主要玉米自交系进行亲缘关系类群划分。本项研究建立了从玉米种子、幼芽以及叶片组织中提取微量DNA的方法。从RAPD引物试验盒A至O共计300个引物中，筛选出对玉米扩增产物具有多态性的引物40个，其中具有特别明显多态性的引物10个。它们是F₃、O₂₀、A₁₉、M₂、M₆、N₁₁、N₁₂、N₁₉、C₇和G₁₄等。依据10个引物扩增谱带建立0，1型数据，计算25个自交系间遗传距离，并进行聚类分析。结果表明：供试的25个自交系共可划分为5个类群。Ⅰ类为四平头血缘系统：包括黄早四、吉853、黄野四、四自四、196、81515、404、H21等共8个；Ⅱ类为瑞德黄马齿血缘系统：包括478、488、3189、7922、8112、B尖8、5005等共7个自交系：Ⅲ类为兰卡斯特血缘系统：包括Mo17、早49、多22等共3个；Ⅳ类为旅大红骨血缘系统：只有E28一个自交系；Ⅴ类共有P78、9502、178、P138、007、P17等6个自交系。这一类群都是由杂交种P78599后代选系而来，与美国另外两个类群瑞德黄马齿系统和兰卡斯特系统关系较远，它们之间选配的杂交组合大多具有较强的杂交优势。这一类群的自交系在我国玉米育种和生产上的应用将进一步扩大。研究结果表明：用RAPD分子标记进行玉米自交系类群划分与系谱法相吻合。通过不同自交系之间杂交，其产量杂交优势的表现，也验证了应用RAPD标记划分的5个不同亲缘关系类群的正确性。

在吉林省中部地区,分析了20个玉米热带系与8个温带系间的160个温热组合的生育期、产量、植株形态特征和穗部性状。结果表明,玉米热带系与合344、四-287等早熟温带系组合的后代,其光敏感性降低明显,尤其是熟期比较早的自交系,反之作用较小;在产量方面,温热组合有一定的增产潜力,相对来说旅大红骨同这批热带系的杂交优势最强,Lancaster最弱;在穗部性状、植株形态性状方面,温热组合的穗部性状与对照差别明显,不同温带系在组合中的作用有较大差异,9046能延长穗长,吉V022能增加穗行数,Mo17能增加行粒数,四-287能减小秃尖、增加百粒质量。

Flowering time is a key agronomic trait determining environmental adaptation and yield potential of crops. The regulatory mechanisms of flowering in maize still remain rudimentary. In this study, we combine expressional, genetic, and molecular studies to identify two homologous SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) transcription factors ZmSPL13 and ZmSPL29 as positive regulators of juvenile-to-adult vegetative transition and floral transition in maize. We show that both ZmSPL13 and ZmSPL29 are preferentially expressed in leaf phloem, vegetative and reproductive meristem. We show that vegetative phase change and flowering time are moderately delayed in the Zmspl13 and Zmspl29 single knockout mutants and more significantly delayed in the Zmspl13/29 double mutants. Consistently, the ZmSPL29 overexpression plants display precocious vegetative phase transition and floral transition, thus early flowering. We demonstrate that ZmSPL13 and ZmSPL29 directly upregulate the expression of ZmMIR172C and ZCN8 in the leaf, and of ZMM3 and ZMM4 in the shoot apical meristem, to induce juvenile-to-adult vegetative transition and floral transition. These findings establish a consecutive signaling cascade of the maize aging pathway by linking the miR156-SPL and the miR172-Gl15 regulatory modules and provide new targets for genetic improvement of flowering time in maize cultivars.© 2023 The Authors. New Phytologist © 2023 New Phytologist Foundation.

\n Flowering time is a fundamental trait of maize adaptation to different agricultural environments. Although a large body of information is available on the map position of quantitative trait loci for flowering time, little is known about the molecular basis of quantitative trait loci. Through positional cloning and association mapping, we resolved the major flowering-time quantitative trait locus,\n Vegetative to generative transition 1\n (\n Vgt1\n ), to an ≈2-kb noncoding region positioned 70 kb upstream of an\n Ap2\n -like transcription factor that we have shown to be involved in flowering-time control.\n Vgt1\n functions as a cis-acting regulatory element as indicated by the correlation of the\n Vgt1\n alleles with the transcript expression levels of the downstream gene. Additionally, within\n Vgt1\n, we identified evolutionarily conserved noncoding sequences across the maize–sorghum–rice lineages. Our results support the notion that changes in distant cis-acting regulatory regions are a key component of plant genetic adaptation throughout breeding and evolution.\n