TRANSCRIPTIONAL REGULATORY NETWORKS CONTROLLING SOYBEAN SEED MATURATION
Jo, L.1, Pelletier, J.M.1, Baden, R.1, Cagliari, A.1, Goldberg, R.B.2 and Harada, J.J.1
1Department of Plant Biology, University of California Davis, Davis, California, USA
2Department of Molecular, Cell, Developmental Biology, University of California Los Angeles, Los Angeles, California, USA
Contact: Leonardo Jo, firstname.lastname@example.org
Soybean (Glycine Max) is the most produced and consumed oilseed in the world. The majority of storage compounds in the soybean seed accumulate in the maturation phase of seed development. Understanding the initiation and establishment of soybean seed maturation may allow us to develop strategies to improve soybean seed quality. We analyzed whole-genome transcriptome datasets to identify two groups of co-expressed genes with spatial and temporal expression patterns that correlate with the maturation program of the soybean seed. In addition, these two groups are highly enriched for genes involved in processes that occur during the maturation of the seed, such as lipid storage and accumulation of storage proteins. Several putative regulators of seed maturation were identified in the clusters, including LEAFY COTYLEDON1 (LEC1), ABSCISIC ACID INSENSITIVE3 (ABI3), BASIC LEUCINE ZIPPER 67 (bZIP67) and ABA-RESPONSIVE ELEMENT BINDING PROTEIN 3 (AREB3). The results suggest that this group of transcription factors play an important role in setting up the maturation program of the soybean seed. In order to identify target genes that are transcriptionally regulated by LEC1, ABI3, bZIP67 and AREB3, we performed chromatin immunoprecipitation and differential gene expression analysis during the maturation stage of soybean seed development. Detailed analysis of target genes showed a complex transcription factor regulatory network in which different combination of transcription factors are involved in distinct biological programs in soybean embryos, such as seed maturation, photosynthesis and embryo morphogenesis. Motif enrichment analysis suggest that a unique set of cis-regulatory elements determine each of these biological programs. A significant enrichment of G-box (CACGTG) and RY (CATGCA) elements in the promoter region of genes that are part of the maturation program was observed. In addition, we observed a spatial organization of these two motifs in cis-regulatory modules near the transcriptional initiation site in the promoters of maturation genes. Moreover, functional analysis of cis-regulatory modules showed that the regions enriched in regulatory motifs are important to determine transcription factor occupancy and activation of maturation related genes. The results obtained in this study are helping us to elucidate the complex transcriptional network that controls soybean seed maturation.