Submitted to: Physiologia Plantarum
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/13/2008
Publication Date: 9/1/2008
Citation: Jain, M., Li, Q., Chourey, P.S. 2008. Cloning and expression analyses of Sucrose non-fermenting-1-Related Kinase 1 (SnRK1b) gene during development of sorghum and maize endosperm, and its implicated role in sugar-to-starch metabolic transition. Physiologia Plantarum. 134:161-173. Interpretive Summary: The SNF-1 gene has long been known as a ‘Master Regulator’ of carbon (C) and nitrogen (N) metabolism in yeast and mammalian cells but little is known in plants. A few recent reports during the last decade, however, suggest a similar role for this gene in various tissue and organs in plants including Arabidopsis. However, there are no data so far on the plant homolog of the SNF1 gene in developing seeds, a major site of C and N metabolism and the sole unit of crop yields. To fill-in this deficiency, we report in cooperation with a scientist from the University of Florida, the first molecular and biochemical study on SNF1 homolog, SnRK1 gene, in developing seeds of maize and sorghum. Gene expression studies strongly suggest that it may perform a regulatory role in establishing source-sink relationship in developing seeds. This basic knowledge is important to scientists who use recombinant DNA technologies to engineer seed metabolism and to increase crop productivity under normal and abnormal growth conditions.
Technical Abstract: A full-length cDNA clone, SbSnRK1b (1530 bp, GenBank accession no. EF544393), encoding a putative serine/threonine protein kinase homologue of yeast (Saccharomyces cerevisiae) SNF1, was isolated from developing endosperm of sorghum [Sorghum bicolor (Moench) L.]. Multiple sequence alignment data showed a phylogenetic affiliation of the sorghum clone with the SnRK1b group of protein kinases that are highly expressed in cereal seed endosperm. The DNA gel blot analyses indicated that SbSnRK1b gene is present as a single- or low copy number gene in sorghum. The RNA and protein gel blot analyses confirmed the expression of SbSnRK1b in developing sorghum caryopses, overlapping with the starch biosynthesis phase, 12- to 24 days-after-fertilization (DAF). In situ hybridization and immunolocalization data resolved the spatial specificity of SbSnRK1b expression in the basal endosperm transfer cell (BETC) layer, the unique port of assimilate unloading in the growing sorghum seed. Expression of SbSnRK1b was also evident in the developing sorghum microspores, coincident with the onset of starch deposition phase. As in sorghum, similar spatiotemporal specificity of SbSnRK1b expression was observed during maize (Zea mays L.) seed development. However, discordant in situ hybridization and immunolocalization data indicated that the expression of SbSnRK1b homologue is under post-transcriptional control during maize endosperm development.