1a. Objectives (from AD-416):
To improve soybean composition, further understanding of the function of cotyledon specific genes is needed. Early soybean seedling establishment is dependent on genes and processes that mobilize the nutrients stored in the cotyledons. This project aims to define the set of genes that are expressed in cotyledon post-germination development, and determine the timing of their expression. 1. Characterize patterns of gene expression in soybean cotyledons during various stages of cotyledon development and senesence. 2. Compare expression patterns of genes in late vegetative stage leaves and cotyledons to identify cotyledon-specific patterns of gene expression during senescence.
1b. Approach (from AD-416):
We have used whole transcriptome RNA sequencing to identify genes that change in expression in coyledons during cotyledon development and are specifically expressed in soybean cotyledons. This year we will commence bioinformatic approaches to assign putative functions to these genes, and to compare the patterns of expression in leaves and cotyledons.
3. Progress Report:
Leaf senescence (or death) is a natural process in the soybean plant, and it is critical that when the leaves die at the end of the growing season that the nutrients (proteins, minerals, carbohydrates) are broken down and redistributed to the developing seeds. A similar process of senescence also occurs after seed germination, when nutrients in the seed storage organs called cotyledons are broken down and serve as an energy source for the growing seedling. This project aims to identify the genes and the genetic program of leaf and cotyledon senescence to find commonalities. This information may help to improve soybean productivity by understanding the timing and control of the process of senescence, to understand the delay of senescence which can be imposed either by the plant (for example, when pods are removed or plants are sterile) or externally by the application of foliar growth regulators which can extend the photosynthetic period of the leaves and lengthen the seed-filling period. A comparison of the data from leaves with that of the cotyledons indicates that the process of senescence is very similar in these two organs, in spite of a few minor differences. Most genes (94% of the genes that were detected) were expressed in both leaves and cotyledons. In cotyledons, in the early stage of development high levels of genes involved in fatty acid degradation, and carbohydrate metabolism in the seed continues into the later stages of cotyledon development and senescence. In leaves, genes encoding molecular transporters (involved in the movement of small molecules between compartments and organs in the plant) increased dramatically in expression during the later stages of senescence while cellular components were being broken down. An important finding for understanding the control of the process of senescence, over 100 members of the MYB family of transcriptional regulators were identified that increased in expression during the senescence process - these MYB "control genes" may turn on a cascade of additional genes that break down and remobilize nutrients.