Association of the molecular regulation of ear leaf senescence/stress response and photosynthesis/metabolism with heterosis at the reproductive stage in maize

Maize exhibits a wide range of heterotic traits, but the molecular basis of heterosis at the reproductive stage has seldom been exploited. Leaf senescence is a degenerative process which affects crop yield and quality. In this study, we observed significantly delayed ear leaf senescence in the reciprocal hybrids of B73/Mo17 and Zheng58/Chang7-2 after silking, and all the hybrids displayed larger leaf areas and higher stems with higher yields. Our time-course transcriptome analysis identified 2,826 differentially expressed genes (DEGs) between two parental lines (PP-DEGs) and 2,328 DEGs between parental lines and the hybrid (PH-DEGs) after silking. Notably, several senescence promoting genes (ZmNYE1, ZmORE1, ZmWRKY53 and ZmPIFs) exhibited underdominant expression patterns in the hybrid, whereas putative photosynthesis and carbon-fixation (ZmPEPC)-associated, starch biosynthetic (ZmAPS1, ZmAPL), gibberellin biosynthetic genes (ZmGA20OX, ZmGA3OX) expressed overdominantly. We also identified 86 transcription factors from PH-DEGs, some of which were known to regulate senescence, stress and metabolic processes. Collectively, we demonstrate a molecular association of the regulations of both ear leaf senescence/stress response and photosynthesis/metabolism with heterosis at the late developmental stage. This finding not only extends our understanding to the molecular basis of maize heterosis but also provides basic information for molecular breeding.