Auxin and Cell Wall Invertase Related Signaling during Rice Grain Development

Sarah French,Yousef Abu-Zaitoon,Heather Nonhebel,Md Uddin,Karina Bennett

doi:10.3390/plants3010095

Abstract

Indole-3-acetic acid (IAA) synthesis is required for grain-fill in maize and appears to be regulated by cell-wall invertase (CWIN) activity. OsYUC12 is one of three IAA biosynthesis genes we previously reported as expressed during early rice grain development, correlating with a large increase in IAA content of the grain. This work aimed to investigate further the role of OsYUC12 and its relationship to CWIN activity and invertase inhibitors (INVINH). The analysis shows a brief peak of OsYUC12 expression early in endosperm development. Meta-analysis of microarray data, confirmed by quantitative expression analysis, revealed that OsYUC12 is coexpressed with OsIAA29, which encodes an unusual AUX/IAA transcription factor previously reported as poorly expressed. Maximum expression of OsYUC12 and OsIAA29 coincided with maximum CWIN activity, but also with a peak in INVINH expression. Unlike ZmYUC1, OsYUC12 expression is not reduced in the rice CWIN mutant, gif1. Several reports have investigated CWIN expression in rice grains but none has reported on expression of INVINH in this species. We show that rice has 54 genes encoding putative invertase/pectin methylesterase inhibitors, seven of which are expressed exclusively during grain development. Our results suggest a more complex relationship between IAA, CWIN, and INVINH than previously proposed.

Highlights

Several recent publications indicate key intersecting signaling roles for indole-3-acetic acid (IAA)and cell wall invertases (CWIN) during cereal grain development
We carried out a comprehensive phylogenetic analysis of invertase inhibitor homologs in rice; we investigated the expression of Os04g49720, a co-ortholog of ZM-INVINH1 previously designated as OsINVINH3 [8]; we extracted and assayed CWIN activity under conditions that have been shown to preserve an enzyme/inhibitor complex [8]
We have shown that rice has at least 54 genes encoding diverse proteins homologous to invertase inhibitors and pectin methylesterase inhibitors (PMEIs)

Summary

Introduction

Cell wall invertases (CWIN) during cereal grain development. ZmYUC1 and related low levels of IAA in the developing grain [1]. (mn1) mutant shows poor grain fill, the low levels of cell wall invertase resulting in a defective basal endosperm transfer layer (BETL) with poorly developed wall in-growths [2]. Forestan et al [4] showed that IAA accumulates in the BETL, aleurone and embryo surrounding region (ESR) just before the endosperm starts to accumulate starch. Both BETL and ESR showed a high level of auxin transporter ZmPIN1 transcript and protein. The relationship between IAA and invertase in rice has not been investigated

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