Abstract

BackgroundHigh post-anthesis (p.a) temperatures reduce mature grain weights in wheat and other cereals. However, the causes of this reduction are not entirely known. Control of grain expansion by the maternally derived pericarp of the grain has previously been suggested, although this interaction has not been investigated under high p.a. temperatures. Down-regulation of pericarp localised genes that regulate cell wall expansion under high p.a. temperatures may limit expansion of the encapsulated endosperm due to a loss of plasticity in the pericarp, reducing mature grain weight. Here the effect of high p.a. temperatures on the transcriptome of the pericarp and endosperm of the wheat grain during early grain-filling was investigated via RNA-Seq and is discussed alongside grain moisture dynamics during early grain development and mature grain weight.ResultsHigh p.a. temperatures applied from 6-days after anthesis (daa) and until 18daa reduced the grain’s ability to accumulate water, with total grain moisture and percentage grain moisture content being significantly reduced from 14daa onwards. Mature grain weight was also significantly reduced by the same high p.a. temperatures applied from 6daa for 4-days or more, in a separate experiment. Comparison of our RNA-Seq data from whole grains, with existing data sets from isolated pericarp and endosperm tissues enabled the identification of subsets of genes whose expression was significantly affected by high p.a. temperature and predominantly expressed in either tissue. Hierarchical clustering and gene ontology analysis resulted in the identification of a number of genes implicated in the regulation of cell wall expansion, predominantly expressed in the pericarp and significantly down-regulated under high p.a. temperatures, including endoglucanase, xyloglucan endotransglycosylases and a β-expansin. An over-representation of genes involved in the ‘cuticle development’ functional pathway that were expressed in the pericarp and affected by high p.a. temperatures was also observed.ConclusionsHigh p.a. temperature induced down-regulation of genes involved in regulating pericarp cell wall expansion. This concomitant down-regulation with a reduction in total grain moisture content and grain weight following the same treatment period, adds support to the theory that high p.a. temperatures may cause a reduction in mature grain weight as result of decreased pericarp cell wall expansion.

Highlights

  • High post-anthesis (p.a) temperatures reduce mature grain weights in wheat and other cereals

  • Mature grain dry weight and grain yield Average mature grain weight in primary tillers was significantly reduced in Experiment 1 by exposure to high p.a. temperature treatments for durations of 4-days or more based on comparison of the least significant differences (LSDs) of the means against the overall mean for each treatment (ANOVA, df = 6, f = 3.54, p = < 0.05)

  • We observed down-regulation of three non-specific LTPs (nsLTPs) at 10daa under high p.a. temperatures compared to expression of these genes at 6daa and 10daa under control temperatures, followed by upregulation at 14daa. We suggest this pattern of expression may reflect the multiple functions of nsLTPs: these genes may be down-regulated under high p.a. temperature conditions at 10daa, reflecting a general reduction in pericarp cell wall extension consistent with the role of nsLTPS as cell wall plasticisers [40], before being upregulated at 14daa in response to high temperatures, possibly to facilitate cuticle development as part of an earlier maturation response of the grain

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Summary

Introduction

High post-anthesis (p.a) temperatures reduce mature grain weights in wheat and other cereals. Cereal grain growth requires both the endosperm and the maternally derived tissue that surrounds it, i.e. the pericarp, to expand during grain filling, and it has been suggested that the pericarp may exert physical control over the size of the wheat grain endosperm by allowing or containing its expansion [10, 12, 13]. This phenomenon, in turn, would be regulated by the potential and ability for expansion of pericarp cell walls. In order to investigate whether high p.a. temperatures reduce grain weight by causing a premature decrease in the ability of the cell walls of the pericarp to expand during development with respect to the endosperm, analysis of the effect of high p.a. temperature on the transcriptome of these tissues is required

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