FUNCTIONAL GENOMICS OF AGRONOMIC TRAITS IN DEVELOPING SEED AND POLLEN IN MAIZE AND SORGHUM
Location: Chemistry Research Unit
Title: Cell wall invertase-deficient miniaturel kernels have altered phytohormone levels
Submitted to: Phytochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 12, 2007
Publication Date: January 1, 2008
Citation: Leclere, S.L., Schmelz, E.A., Chourey, P.S. 2008. Cell wall invertase-deficient miniaturel kernels have altered phytohormone levels. Phytochemistry. 69:692-699.
Interpretive Summary: Despite the enormous agronomic importance of seed weight, very little is still known about genes that control this trait; in particular, the control of cell number and cell size in developing seeds – the ultimate determinants of crop productivity. Our past cooperative studies at the CMAVE, USDA ARS, SAA and the University of Florida have shown that the miniature1 (Mn1) gene in maize encodes a major enzyme that acts as a gatekeeper of sugars that enter developing seeds, and thus determine its sink size and sink strength. Here in this report, we show that the Mn1 gene also affects, directly or indirectly, the levels of a major plant hormone, an auxin, indole acetic acid (IAA), which is known to affect many basic processes of growth and development. Additionally, we show that the loss-of-function mutations at the Mn1 gene down-regulate a gene that is critical in the biosynthesis of IAA. To the best of our knowledge, this is the first example of a close linkage between genes of sugar and hormone biosynthesis in developing seeds. Further understanding of this interaction or crosstalk between these two distinct pathways is essential (work in progress) for fundamental understanding of seed development, an essential prerequisite for genetic manipulation towards increased crop productivity.
The Zea mays (maize) Mn1 (miniature1) locus encodes the cell wall invertase INCW2, which is localized predominantly in the basal endosperm transfer layer (BETL) of developing kernels and catalyzes conversion of sucrose into glucose and fructose. Mutations in Mn1 result in numerous changes that include a small kernel phenotype resulting from both decreased cell size and number. To explore the pleiotropic effects of this mutation, we investigated the levels of indole-3-acetic acid (IAA), abscisic acid (ABA), salicylic acid (SA), and jasmonic acid (JA) in basal regions, upper regions, and embryos of developing kernels in the inbred line W22. We measured phytohormones from 6 to 28 days after pollination (DAP) in wild type (WT) and two alleles of mn1, mn1'1 and mn1'89. IAA was the predominant hormone in kernels, with WT levels of free IAA accumulating over time to more than 2 µg/g of fresh weight. Kernels of mn1'1 accumulated up to ten-fold less IAA than WT, and levels of IAA sugar conjugates were similarly reduced. Although less abundant, differences were also observed in levels of ABA, JA, and SA between WT and the mn1 alleles. SA levels were increased by as much as ten-fold in mn1'1, and mn1'89 displayed intermediate SA levels at most timepoints. These findings indicate that invertase-mediated sucrose cleavage directly or indirectly regulates the levels of key plant hormones during seed development.