Submitted to: Molecular Plant
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/27/2010
Publication Date: 11/1/2010
Citation: Chourey, P.S., Li, Q., Kumar, D. 2010. Sugar - hormone crosstalk in seed development: Two redundant pathways of IAA biosynthesis are regulated differentially in the invertase-deficient miniature1 (mn1) seed mutant in maize. Molecular Plant. 3:1026-1036. Interpretive Summary: There is a large body of knowledge on sugar metabolism and its role in seed size determination but little is known about hormones and, more importantly, the orchestration of sugar and hormone signaling pathways that ultimately determine sink strength and normal seed development. A cooperative investigation between scientists from Chemistry Unit, CMAVE, USDA ARS and the University of Florida, at Gainesville, FL, based on genetics, molecular biology and bioinformatics provide critical insights that show for the first time two redundant pathways of a hormone, auxin (IAA), biosynthesis in developing maize seeds, and that sugar metabolism may regulate their expression. Overall the results show multiple gens of IAA biosynthesis in maize seed; further studies are needed to better understand their roles in seed development and crop yields.
Technical Abstract: The miniature1 (mn1) seed phenotype is a loss-of-function mutation at the Mn1 locus that encodes a cell wall invertase; its deficiency leads to pleiotropic changes including altered sugar levels and decreased levels of IAA throughout seed development. To understand the molecular details of such sugar-hormone relationship, we have initiated studies on IAA biosynthesis genes in developing seeds of maize. Two tryptophan-dependent redundant pathways of IAA biosynthesis, tryptamine (TAM) and indole-3-pyruvic acid (IPA), are of particular interest. We report here on molecular isolation and characterization of an endosperm-specific ZmTARelated1 (ZmTar1) gene of the IPA branch; we have also reported recently on ZmYuc1 gene in the TAM branch. Comparative gene expression analyses here have shown that (a) the ZmTar1 transcripts were ~ 10-fold higher levels than the ZmYuc1 throughout the endosperm development; (b) although both genes showed the highest level of expression at 8 - 12 days after pollination (DAP) coincident with an early peak of IAA levels, the two showed highly divergent (antagonistic) response at 12 and 16 DAP but similar pattern at 20 and 28 DAP in the Mn1 and mn1 endosperm. Overall, these data suggest that developing seeds may modulate sink strength by, among other factors, altering auxin biosynthesis in response to sucrose metabolism and developmental signals.