Pectins, the major components of cell walls in plants, are synthesized and secreted to cell walls as highly methyl-esterified polymers and then demethyl-esterified by pectin methylesterases (PMEs). The PMEs are spatially regulated by pectin methylesterase inhibitors (PMEIs). In this study, 43 and 49 putative PME and PMEI genes were identified in maize, respectively. Gene structure and motif analysis revealed that members in the same paralogous pairs or in the same subgroup generally had common motif compositions and gene structure patterns, which indicates functional similarity between the closely related ZmPME/PMEI genes. Gene ontology annotation analysis showed that most of the ZmPME/PMEI genes are involved in cell wall modification and pectin catabolic process with molecular functions of pectinesterase or pectinesterase inhibitor activities. There are 35 ZmPME/PMEI genes expressed higher in anthers than in other tissues from the NimbleGen maize microarray data, and the semiq-RT-PCR assay revealed most of these ZmPME/PMEIs specially expressed in anthers and pollens, indicating they possibly had role in anther and pollen development. In addition, these ZmPME/PMEI genes were highly expressed in the fertile anthers, while lowly or no expressed in sterile anthers. This further indicated these genes might be involved in the development of anther and pollen.

Maize seedlings are sensitive to low temperatures, and genetic mapping for chilling tolerance at the seedling stage with genetically diverse populations would facilitate the genetic improvement of this important trait. In this study, quantitative trait loci (QTL) mapping for four chilling tolerancerelated traits at the seedling stage was conducted via a genome-wide association study (GWAS) with 338 testcrosses. A total of 32 significant loci and 36 stress tolerance-related candidate genes were identified, though none of them have been revealed by QTL mapping using maize inbred lines in previous reports. Moreover, expression of ten of the candidate genes was induced by chilling stress in a maize hybrid, though only a few of these genes were upregulated in its tolerant parent. These implied that heterosis might be involved in maize chilling tolerance. To further evaluate the importance of heterosis in chilling tolerance at the seedling stage, genetic mapping for chilling tolerance was conducted using an F 2:3 population derived from the two inbred lines used for the gene expression assay. Of the seven QTL revealed, six loci showed partial dominance or over-dominance effects. Results from this study demonstrate that heterosis plays an important role in chilling tolerance in maize seedlings.Maize (Zea mays L.) is an important food, energy, forage and industrial crop. However, chilling (0-15 °C) has become a major environmental factor that limits maize production and its distribution. Chilling stress affects germination, seedling growth, early leaf development and overall maize crop growth and productivity 1 . In particular, maize seedlings are the most sensitive to chilling stress during the transition phase from heterotrophic to autotrophic growth 2 . Therefore, elucidating the mechanism of maize chilling tolerance at the seedling stage (3-leaf stage) will help to genetically improve this trait.Yield performance is usually used to evaluate stress tolerance at the reproductive stage, while at the seedling stage, it mainly relies on morphological-physiological traits. Physiological traits, such as photosynthetic performance 3-5 , tissue water content, and levels of abscisic acid (ABA) and antioxidants 3 , usually respond to low temperatures earlier than changes in morphological traits and are extensively used as indicators of chilling tolerance. Additionally, as a kind of compatible solute to increase the osmotic potential and stabilize macromolecular structure, soluble sugar content can also be a good index for stress tolerance evaluation 6 . At the morphological level, chilling stress causes decreased growth rates, leaf elongation and dry weights 2 . Chilling stress decreases root hydraulic conductance 7 and often results in water-stress symptoms. Root development in chilling-sensitive maize seedlings was found to be distinctly reduced under chilling stress, and the root-to-shoot ratio in chilling-sensitive inbred plants decreased under chilling stress conditions at the 2-to 3-leaf stage 8 . Because physiological t...

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Summary Tassel branch number (TBN) is one of the important agronomic traits that directly contribute to grain yield in maize (Zea mays L.), and identification of genes precisely regulating TBN in the parental lines is important for maize hybrid breeding. In this study, a quantitative trait nucleotide (QTN), QDtbn1, related to tassel branch number was identified using a testcrossing association mapping population through association mapping with the Indels/SNPs in the 5′‐UTR (untranslated region) of Zm00001d053358, which encodes a Kelch repeat‐containing F‐box protein. QDtbn1 was further confirmed to be associated with TBN by a dominant model using an F2 population, and over‐expressing of the candidate gene resulted in a decreasing of TBN, implying that QDtbn1 was governed by the candidate gene with a negative model. This makes QDtbn1 very useful in maize hybrid breeding. QDtbn1 could interact with a maize Skp1‐like protein and a SnRK1 protein, and the SnRK1 could also interact with a SnRK2.8 protein. In addition, quantitative real‐time PCR assay showed that five substrates of SnRK2 were down‐regulated in the over‐expressed plants. These imply that the SCF (Skp1/Cul1/F‐box protein/Roc1) complex and ABA signal pathway might be involved in the modulation of TBN in maize.

Cytoplasmic male sterility (CMS) is extensively used in maize hybrid production, and identification of genes related to fertility restoration for CMS is important for hybrid breeding. The fertility restoration of S type CMS is governed by several loci with major and minor effects, while the mechanism of fertility restoration for CMS-S is still unknown. In this study, BSR-Seq was conducted with two backcrossing populations with the fertility restoration genes, Rf3 and Rf10, respectively. Genetic mapping via BSR-Seq verified the positions of the two loci. A total of 353 and 176 differentially expressed genes (DEGs) between the male fertility and male sterile pools were identified in the populations with Rf3 and Rf10, respectively. In total, 265 DEGs were co-expressed in the two populations, which were up-regulated in the fertile plants, and they might be related to male fertility involving in anther or pollen development. Moreover, 35 and seven DEGs were specifically up-regulated in the fertile plants of the population with Rf3 and Rf10, respectively. Function analysis of these DEGs revealed that jasmonic acid (JA) signal pathway might be involved in the Rf3 mediated fertility restoration for CMS-S, while the small ubiquitin-related modifier system could play a role in the fertility restoration of Rf10.