FUNCTIONAL GENOMICS OF AGRONOMIC TRAITS IN DEVELOPING SEED AND POLLEN IN MAIZE AND SORGHUM
Location: Chemistry Research Unit
Title: Discovery of Genes Expressed In Basal Endosperm Transfer Cells in Maize Using 454 Transcriptome Sequencing
Submitted to: Plant Molecular Biology Reporter
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 20, 2011
Publication Date: February 16, 2011
Citation: Xiong, Y., Li, Q., Kang, B., Chourey, P.S. 2011. Discovery of Genes Expressed In Basal Endosperm Transfer Cells in Maize Using 454 Transcriptome Sequencing. Plant Molecular Biology Reporter. 29:835-847.
Interpretive Summary: A developing maize seed is comprised of two distinctive tissues, endosperm and embryo; the former is a storage organ for starch and proteins and is of huge economic importance as it is a major contributor of food, feed and biofuel production associated with this crop. Endosperm is anatomically comprised of four cell types; one of these is the basal endosperm transfer layer (BETL) which is most well developed in maize among all cereal crops. Our previous work has shown that loss-of-function mutation of a certain BETL gene leads to highly shriveled or miniature seeds; thus, BETL is critical in normal seed development. However, there is no global analysis or a catalog of all genes that are expressed in the BETL. This report based on a cooperative investigation between scientists from Chemistry Unit, CMAVE, SAA, USDA ARS and the University of Florida, at Gainesville, FL, greatly minimizes this deficiency by providing not only a simple procedure to isolate BETL but also the first high throughput detailed identification of a total of 2,473 Expressed Sequence Tags (ESTs), each representing a partial gene, expressed in the BETL. In silico analyses of the BETL ESTs show that they are predominantly associated with functions related to nutrient transport, disease resistance, mitochondrial activity, hormone biosynthesis, and signaling activity between the mother plant and the developing seed. Future studies are aimed to analyze some of these most abundantly expressed genes to better understand their structure and function, and finally the BETL itself to enhance seed size and quality, an ultimate unit of crop productivity.
Basal endosperm transfer cells (BETCs) constitute one of the four cell types in an endosperm with a major role in solute acquisition and transport functions from the mother plant. The BETCs with their wall-in-growth (WIG) feature that greatly increase plasma membrane area of each cell are critical for seed development in all cereals. Although several BETC-specific genes are described in maize, there is as yet no global analysis or a catalog of all genes expressed in the BETCs. First, we developed a simplified manual dissection method to microdissect BETCs from developing kernels at 12 days after pollination, a stage of one of the most active metabolic phases of seed development. High quality RNA was isolated from microdissected BETCs and used in cDNA synthesis, 454 sequencing and EST assembly, which led to a complement of 2473 ESTs with an average length of 218 bases. Validation of the BETC-specificity of some of the 454 sequences was done by qRT-PCR and by in situ hybridization. Based on several criteria, we suggest that our method has yielded the BETC-specific RNAs. Functional annotation and categorization of the 2,473 unique sequences showed that the largest proportion of the BETC genes were engaged in functions related to mitochondrial activity, protein metabolism, nucleotide and protein binding activities and defense functions.