Physiological and omics analysis of maize inbred lines during late grain development.

BACKGROUND: There were significant differences in the change of moisture content and grain composition at the late stage of grain development among different maize varieties, but the regulation mechanism is not clear. OBJECTIVE: To explore the key genes causing the variation in physiological traits of two typical maize inbred lines in late grain development. METHODS: The grains at different development stages were selected as materials to determine the content of water, sucrose, starch and ABA. Transcriptomic and proteomic analysis of the materials were performed to screen relevant genes. RESULTS: The grain dehydration rate and the content of sucrose, starch and ABA were showed significant differences between two varieties in the late stage of grain development. The enrichment analysis of common differentially expressed genes (proteins) showed that most of the genes (proteins) were enriched in the extracellular region. The downregulated genes were mainly concentrated in carbohydrate metabolism and lipid metabolism, while the upregulated genes were mainly in response to stress. Furthermore, this study also identified many key candidate genes (dehydrin genes, pathogenesis-related genes, sucrose synthase and secondary metabolites related genes) related to late grain development of maize. CONCLUSIONS: The suggested genes related to late grain development of maize can be candidates for further functional study.

Identification and Characterization of microRNAs during Maize Grain Filling.

The grain filling rate is closely associated with final grain yield of maize during the period of maize grain filling. To identify the key microRNAs (miRNAs) and miRNA-dependent gene regulation networks of grain filling in maize, a deep-sequencing technique was used to research the dynamic expression patterns of miRNAs at four distinct developmental grain filling stages in Zhengdan 958, which is an elite hybrid and cultivated widely in China. The sequencing result showed that the expression amount of almost all miRNAs was changing with the development of the grain filling and formed in seven groups. After normalization, 77 conserved miRNAs and 74 novel miRNAs were co-detected in these four samples. Eighty-one out of 162 targets of the conserved miRNAs belonged to transcriptional regulation (81, 50%), followed by oxidoreductase activity (18, 11%), signal transduction (16, 10%) and development (15, 9%). The result showed that miRNA 156, 393, 396 and 397, with their respective targets, might play key roles in the grain filling rate by regulating maize growth, development and environment stress response. The result also offered novel insights into the dynamic change of miRNAs during the developing process of maize kernels and assisted in the understanding of how miRNAs are functioning about the grain filling rate.

Proteomic identification of genes associated with maize grain-filling rate.

Grain filling during the linear phase contributes most of the dry matter accumulated in the maize kernel, which in turn determines the final grain yield. Endosperms and embryos of three elite maize hybrids (Zhengdan 958, Nongda 108, and Pioneer 335) were sampled 17, 22, 25, and 28 days after pollination, during the linear phase of grain filling, for proteomic analysis to explore the regulatory factors critical for grain filling rate. In total, 39 and 43 protein spots that showed more than 2-fold changes in abundance at P<0.01 between any two sampling stages in the endosperm and embryo were analyzed by protein mass spectrometry. The changing patterns in expression index of these proteins in the endosperm were evenly distributed, whereas up-regulation patterns predominated (74%) in the embryo. Functional analysis revealed that metabolism was the largest category, represented by nine proteins in the endosperm and 12 proteins in the embryo, of the proteins that significantly changed in abundance. Glycolysis, a critical process both for glucose conversion into pyruvate and for release of free energy and reducing power, and proteins related to redox homeostasis were emphasized in the endosperm. Additionally, lipid, nitrogen, and inositol metabolism related to fatty acid biosynthesis and late embryogenesis abundant proteins were emphasized in the embryo. One protein related to cellular redox equilibrium, which showed a more than 50-fold change in abundance and was co-localized with a quantitative trait locus for grain yield on chromosome 1, was further investigated by transcriptional profile implying consistent expression pattern with protein accumulation. The present results provide a first step towards elucidation of the gene network responsible for regulation of grain filling in maize.

Proteomic analysis of heterosis during maize seed germination.

Heterosis is observed for most phenotypic traits and developmental stages in many plants. In this study, the embryos, from germinating seeds after 24 h of soaking, for five elite maize hybrids and their parents were selected to unravel the genetic basis of heterosis using 2-D proteomic method. In total, 257 (80.06%), 363 (58.74%), 351 (79.95%), 242 (54.50%), and 244 (46.30%) nonadditively expressed proteins were identified in hybrids Zhengdan 958, Nongda 108, Yuyu 22, Xundan 20, and Xundan 18, respectively. The nonadditive proteins were divided into above high-parent (++; 811, 55.66%), high-parent (+; 121, 8.30%), partial dominance (+-; 249, 17.09%), low-parent (-; 30, 2.06%), below low-parent (- -; 62, 4.26%), and D (different; 184, 12.63%) expression patterns. The observed patterns indicate the important roles of dominance, partial dominance, and overdominance in regulating seed germination in maize. Additionally, 54 different proteins were identified by mass spectrometry and classified into nine functional groups: metabolism (9), cell detoxification (8), unknown functional proteins (8), chaperones (7), signal transduction (6), development process (5), other (5), transporter (3), and stress response (3). Of these, the most interesting are those involved with germination-related hormone signal transduction and the abscisic acid and gibberellin regulation networks.