Senescence Associated Genes Identified By Expression Profiling in Glycine max Cotyledons and Trifoliate Leaves.

Following germination, the developing soybean seedling relies on the nutrient reserves stored in the cotyledons to sustain heterotrophic growth. Likewise, a developing seed relies on the transport of nutrients from the trifoliate leaves. Before cotyledon and leaf tissues senesce, the nutrients must be mobilized and transported to other parts of the plant. We used an RNAseq approach to compare levels of gene expression throughout leaf and cotyledon development in Glycine max. Over 61,000 transcripts were found to be expressed during the course of both leaf and cotyledon development. Of those transcripts, 2,500 transcripts were expressed in a tissue specific pattern. Differentially expressed genes between two stages of leaf/cotyledon development were determined using three different expression analysis packages, and genes with robust changes in expression were identified. Of the genes that were differentially expressed between both later stage tissues, 90% of them had the same directionality of change, suggesting that the mechanisms of senescence are conserved between tissues. From this analysis we were able to divide the process of senescence into distinct stages and identify genes critical for senescence. Pathway analysis was used to identify senescence-related processes. Highly responsive genes and candidate regulatory genes will be discussed.