Submitted to: Journal of Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/2/2006
Publication Date: 2/18/2008
Citation: Mukesh, J., Chourey, P.S., Li, Q., Pring, D.R. 2008. Expression of cell wall invertase and several other genes of sugar metabolism in relation to seed development in sorghum (Sorghum bicolor). Journal of Plant Physiology. 165(3): 331-344. Interpretive Summary: Plants run on sucrose. After its synthesis in leaves and subsequent transport to developing seeds, sucrose is cleaved to simple sugars by an enzyme cell wall invertase (CWI). Our previous studies in maize have shown that CWI is critical in controlling the flux of sucrose that enters developing seeds; and, a loss of this enzyme can greatly reduce seed size and weight, an ultimate unit of crop yields. No such information is available for sorghum, a dry-land cereal which is molecularly closely related to maize. The current study is a collaborative effort of scientists at the University of Florida and the ARS at CMAVE laboratories, Gainesville, FL. Our results show that there are at least four genes (only two in maize), which are highly similar to each other and to the maize CWI genes that code for this enzyme in developing seeds. All genes are expressed simultaneously at the base of the seed, including the maternal tissues. Further studies are aimed to better understand the role of these genes in sorghum seed development and what role, if any, they may have in making sorghum so much more tolerant to heat and drought stress relative to maize. This basic knowledge is important to scientists who use recombinant DNA technologies to engineer seed metabolism and to increase crop productivity under heat and drought conditions.
Technical Abstract: We report isolation of four near full-length cDNA clones of cell wall invertase (CWI) genes, SbIncw1, -2, -3 and -4, from developing caryopses of grain sorghum [Sorghum bicolor (L.) Moench]. RNA blot analyses of developing caryopses, including glumes (maternal tissue appended to the seeds) at various stages of development showed an overlapping pattern of expression of these four genes. Deduced amino acid sequences of the four clones indicated the conservation of cysteine catalytic and glycosylation motifs, the hallmarks of CWI genes, and significant sequence homology to the maize ortholog ZmIncw2. Real time quantitative PCR analyses showed that transcript abundance of maize ortholog ZmIncw2 was several orders of magnitude higher than ZmIncw1 ortholog in lower parts of the developing endosperm in the developing seed. Expression of the ZmIncw1 ortholog was restricted primarily to the glumes. The protein and enzyme activity data corroborated the transcript expression data. Protein gel blot analysis using polyclonal maize INCW1 antibodies showed a single polypeptide of 72 kDa. Additionally, we report transcription profiles of several genes related to sugar-to-starch metabolism in developing seeds of sorghum.