Cell wall invertase-deficient miniature1 kernels have altered phytohormone levels

Abstract

The Zea mays (maize) miniature1 ( Mn1) 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 10-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 10-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.