Normalizing Developmental Patterns of Gene Expression in Maize Kernels.

Gene expression profiling is a particularly valuable approach to identify transcriptional processes that regulate metabolic and developmental responses to high temperature and water deficit stress in maize (Zea mays L.) kernels. Because such abiotic stresses can alter the pattern of kernel development dramatically, the physiological relevance of gene expression data may be difficult to assess if profiles are not aligned to a common developmental frame of reference. We have shown that kernels from a wide range of genotypes and treatments follow a common pattern of development when dry matter accumulation and water content are expressed on a moisture content basis. Our objective was to determine whether kernel moisture content provided a superior basis for normalizing gene expression patterns in developing kernels. We quantified the expression of 12 genes related to starch biosynthesis, storage protein synthesis, and seed maturation in developing kernels on well-watered and water-stressed plants of inbred B73. The water deficit, imposed by withholding water prior to rapid grain filling, shortened the duration of dry matter accumulation resulting in a 21% reduction in final seed dry weight. Starch, protein, and oil concentrations, however, were not affected. The susceptibility of kernel starch to enzymatic hydrolysis was enhanced by 15% in the stressed kernels relative to the controls, which suggests more subtle changes in the physical properties or composition of starch granules might have occurred. This poster presents our preliminary analysis of development- and stress-related patterns of gene expression normalized on a temporal and kernel moisture content basis. This approach provides a rational basis to distinguish unique responses to abiotic stress from those associated with accelerated, yet normal, kernel development.