Effects of drought on gene expression in maize reproductive and leaf meristem tissue revealed by RNA-Seq.

Akshay Kakumanu,Arjun Krishnan,Andy Pereira,Elijah Myers,Curtis Klumas,Madana M R Ambavaram,Utlwang Batlang,Ruth Grene

doi:10.1104/pp.112.200444

Akshay Kakumanu, Arjun Krishnan + Show 6 more

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https://doi.org/10.1104/pp.112.200444

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Abstract

Drought stress affects cereals especially during the reproductive stage. The maize (Zea mays) drought transcriptome was studied using RNA-Seq analysis to compare drought-treated and well-watered fertilized ovary and basal leaf meristem tissue. More drought-responsive genes responded in the ovary compared with the leaf meristem. Gene Ontology enrichment analysis revealed a massive decrease in transcript abundance of cell division and cell cycle genes in the drought-stressed ovary only. Among Gene Ontology categories related to carbohydrate metabolism, changes in starch and Suc metabolism-related genes occurred in the ovary, consistent with a decrease in starch levels, and in Suc transporter function, with no comparable changes occurring in the leaf meristem. Abscisic acid (ABA)-related processes responded positively, but only in the ovaries. Related responses suggested the operation of low glucose sensing in drought-stressed ovaries. The data are discussed in the context of the susceptibility of maize kernel to drought stress leading to embryo abortion and the relative robustness of dividing vegetative tissue taken at the same time from the same plant subjected to the same conditions. Our working hypothesis involves signaling events associated with increased ABA levels, decreased glucose levels, disruption of ABA/sugar signaling, activation of programmed cell death/senescence through repression of a phospholipase C-mediated signaling pathway, and arrest of the cell cycle in the stressed ovary at 1 d after pollination. Increased invertase levels in the stressed leaf meristem, on the other hand, resulted in that tissue maintaining hexose levels at an "unstressed" level, and at lower ABA levels, which was correlated with successful resistance to drought stress.

Highlights

Drought stress affects cereals especially during the reproductive stage
To advance our understanding of responses to drought stress in early embryos, we report here on the results of an RNA-Seq transcriptome analysis using Illumina deep sequencing of RNA populations obtained from well-watered and drought-stressed leaf meristem and pollinated ovaries of the fully sequenced maize (B73) genotype
The degree of drought stress was determined by monitoring soil moisture content, relative water content, chlorophyll fluorescence, and CO2 gas exchange in the moisture content decreased from leaves

Summary

Introduction

Drought stress affects cereals especially during the reproductive stage. The maize (Zea mays) drought transcriptome was studied using RNA-Seq analysis to compare drought-treated and well-watered fertilized ovary and basal leaf meristem tissue. Cell wall invertase itself is likely part of a signaling pathway, since it is known to form a complex in the nucleus with PIP5K9, a component of the phosphoinositol signaling system (Lou et al, 2007) It is possible, that functions related to sugar supply, as well as those involving various sugar signaling pathways, are influenced under drought stress in developing reproductive tissue. Effects of drought on sugar signaling/metabolism, auxin- and ethylene-related processes, and trehalose metabolism have all been proposed as part of the chain of events surrounding embryo abortion in maize or rice (Yu and Setter, 2003; Boyer and McLaughlin, 2007; Jain and Khurana, 2009; Feng et al, 2011; Setter et al, 2011) Most of these studies, such as those cited above, were conducted on fertilized ovaries from 8 DAP onward, yet drought-mediated embryo abortion is observed immediately after pollination. The bulk of the tissue within the kernel is maternal in origin at 1 DAP (Andersen et al, 2002)

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