Understanding the Molecular Regulation of Senescence in Glycine max

A leaf undergoes several important changes during development. As the newly initiated leaf expands and gains photosynthetic competency, it undergoes a transition from nutrient sink to source. Later it undergoes a natural aging process called senescence, where nutrients that remain in the leaf are mobilized and exported to new sinks such as the seed. The time and length of senescence is crucial to seed quality and overall plant yield.  However plants that do not produce a sink, such as depodded and sterile plants have a delayed senescence (or a “stay green” phenotype). An RNA-seq timecourse approach was used to compare levels of gene expression in normal, depodded, and sterile trifoliate leaves and cotyledons to identify transcriptional changes throughout development. Over 38,000 transcripts were found to be expressed during the course of both leaf and cotyledon development. Differentially expressed genes were identified between stages of the timecouse in all samples, and were placed into developmental profiles. Analysis of the enrichment of biological functions within genes sharing common expression profiles highlights the main processes occurring within these defined temporal windows of normal leaf and cotyledon development. Genes expressed during the later stages of both tissues shared common functions, suggesting that the mechanisms of senescence are conserved between tissues. Over 1,000 genes were identified with predicted regulatory functions that may have a role in control of leaf or cotyledon senescence. Biological functions identified during normal leaf developments were compared with depodded and sterile plants to identify differences between the tissues.