Water Stress and Shade Elicit Similar Convergent Responses in Maize Kernel Development and Gene Expression During Early Post-Pollination.

Maize crop yields are substantially diminished by drought during early phases of kernel development. Kernel development is also affected by stresses which limit photosynthate availability, such as high plant density and shade. To advance our understanding of the mechanisms by which these stresses affect kernel development, we subjected potted maize plants in the greenhouse to water stress and shade from 1 to 9 days after pollination and determined evapotranspiration, root growth in deep pots, carbohydrates and ABA in leaves and kernel tissues, and profiled expression of gene transcripts in kernel tissues with RNA-seq. Root development was decreased by shade, whereas it was increased by severe water stress (WS). Both severe WS and shade increased ABA levels in kernel tissues. A large fraction of differentially expressed genes in pedicel-placenta tissues of kernels were affected similarly by severe WS and shade, including genes involved in synthesis and response to ABA, carbohydrates, trehalose, and ethylene. Differential expression in response to mild WS was intermediate or minimal. In endosperm-nucellus, expression of genes in these categories was strongly affected by shade, but less so by severe WS. We conclude that the similarity of ABA accumulation and gene expression in pedicel-placenta of severe WS and shade indicates that this tissue likely plays a pivotal role in kernel set decisions.