Temporally modular gene expression during cotyledon development.

The regulation of cotton embryogenesis has been addressed by measuring the abundance of 47 mRNAs in cotyledons from the late cotyledon stage through early germination. There are at least 11 distinct classes of coordinately expressed mRNAs. Their expression patterns appear to result from unique combinations of five temporal abundance components. These are associated with the cotyledon stage, the endogenous concentration of free abscisic acid, maturation (reserve accumulation), ovule abscission, and germination. This modularity suggests that only a few global regulatory factors orchestrate gene expression with many genes responding to several of them. Significant expression associated only with postabscission or free abscisic acid is restricted to that of the Lea mRNAs earlier suggested to be a component of the embryo's preparation for desiccation.