Submitted to: Planta
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/4/2005
Publication Date: 7/21/2005
Citation: Chourey, P.S., Jain, M., Li, Q., Carlson, S.J. 2005. Genetic control of cell wall invertases in developing endosperm of maize. Planta. 223:159-167. Interpretive Summary: Sugar metabolism and its control are critical to all parts of the plant, including developing seed - a major site of sugar utilization and also an important unit of crop yield. The enzyme cell wall invertase is one of the most important enzymes of sucrose metabolism because it cleaves sucrose to simple sugars prior to its appropriate utilization in developing seeds. Loss of this function through mutation leads to severe reductions in plant growth and crop productivity. Yet, very little is known on the genetic control, in particular the number of genes that encode this enzyme, in developing seeds. The current report remedies this deficiency. Collaborative efforts between the ARS scientists at CGERU, CMAVE, Gainesville, FL and the University of Florida, show that there are at least two genes that code for this enzyme in developing seeds. Each gene has a unique function because of their both cell-and time-specific patterns of gene expression. This basic knowledge is important to a group of scientists who use recombinant DNA technologies to engineer seed metabolism and /or seed mass to increase crop productivity.
Technical Abstract: We show here that the total invertase activity in developing seed of maize is due to two cell wall invertase (CWI) genes, Incw1 and Incw2 (Mn1). Our previous results have shown that loss-of-function mutations at the Mn1 locus lead to the miniature-1 (mn1) seed phenotype, marked by a loss of >70% of seed weight at maturity. The mn1 seed mutant is, however, non-lethal presumably because it retains throughout seed development a residual low level, ~1%, of the total CWI activity relative to the Mn1 endosperm. Evidence here shows that the residual activity in the mn1 mutant is encoded by the Incw1 gene. RNA level analyses, especially quantitative real-time -PCR (q-PCR) studies, showed significant spatial and temporal heterogeneity in the expression of the two CWI genes in developing endosperm. The Mn1-encoded Incw2 transcripts were seen at the highest levels in basal region (the sugar unloading zone) during the early phase of cell division and elongation in endosperm. By contrast, the highest levels of Incw1 transcripts were seen in the storage phase in both upper (storage cells) and lower parts of endosperm. Collectively, the data suggest an important role for apoplastic cleavage of sucrose throughout the duration of seed development; and, of the two isoforms, the INCW2 appears to control metabolic flux of sugar utilization in the developing endosperm.