Abstract
BackgroundDuring maize early kernel development, the dramatic transcriptional reprogramming determines the rate of developmental progression, and phytohormone plays critical role in these important processes. To investigate the phytohormone levels and transcriptome reprogramming profiles during maize early kernel development, two maize inbreds with similar genetic background but different mature kernel sizes (ILa and ILb) were used.ResultsThe levels of indole-3-acetic acid (IAA) were increased continuously in maize kernels from 5 days after pollination (DAP) to 10 DAP. ILa had smaller mature kernels than ILb, and ILa kernels had significantly lower IAA levels and significantly higher SA levels than ILb at 10 DAP. The different phytohormone profiles correlated with different transcriptional reprogramming in the two kernels. The global transcriptomes in ILa and ILb kernels were strikingly different at 5 DAP, and their differences peaked at 8 DAP. Functional analysis showed that the biggest transcriptome difference between the two kernels is those response to biotic and abiotic stresses. Further analyses indicated that the start of dramatic transcriptional reprogramming and the onset of significantly enriched functional categories, especially the “plant hormone signal transduction” and “starch and sucrose metabolism”, was earlier in ILa than in ILb, whereas more significant enrichment of those functional categories occurred at later stage of kernel development in ILb.ConclusionsThese results indicate that later onset of the significantly enriched functional categories, coincide with their stronger activities at a later developmental stage and higher IAA level, are necessary for young kernels to undergo longer mitotic activity and finally develop a larger kernel size. The different onset times and complex interactions of the important functional categories, especially phytohormone signal, and carbohydrate metabolism, form the most important molecular regulators mediating maize early kernel development.
Highlights
During maize early kernel development, the dramatic transcriptional reprogramming determines the rate of developmental progression, and phytohormone plays critical role in these important processes
ILa kernels at 10 days after pollination (DAP) had lower indole-acetic acid (IAA) levels and higher salicylic acid (SA) levels than ILb kernels Two maize lines, ILa (JN14–7-22) and ILb (JN14–7-13), were developed from a single F2 progeny ear of a self-crossed hybrid after another three rounds of self-crossing
At 8 DAP, IAA was detected in low abundance in kernels of both inbreds; the IAA level was slightly higher in ILa kernels than in ILb kernels
Summary
During maize early kernel development, the dramatic transcriptional reprogramming determines the rate of developmental progression, and phytohormone plays critical role in these important processes. Maize kernel development begins with double fertilization of a haploid egg cell and dikaryotic central cell to produce two filial structures: a diploid embryo and triploid endosperm. This complex biological process can be divided into three phases: early development, reserve filling and dehydration, and phyohormones play vital roles during this process [1,2,3,4]. The endosperm of mutant de maize kernels displays impaired IAA biosynthesis, large reductions in free IAA levels throughout endosperm development, and approximately ~ 40% less dry mass than wild type, suggesting a disruption of nutrient uptake [15]
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