Abstract/Summary

High post-anthesis (p.a.) temperatures reduce mature grain weight and consequently yield in wheat. However, the mechanisms behind this reduction are still not entirely known. It has recently been suggested that a premature maturation of the pericarp under high p.a. temperatures could result in a loss of cell wall plasticity in the layer which may restrict endosperm expansion and reduce grain weight. In order to test this hypothesis, 4 controlled environment experiments were performed using the wheat cultivar Cadenza. The effect of high p.a. temperatures on various aspects of wheat grain development were investigated using methods including grain dimension and weight analysis, immunofluorescence microscopy of endosperm cells in addition to the distribution and form of cell wall homogalacturonan (HG) and RNA-Seq analysis of the transcriptome of high p.a. temperature treated grain. Mature grain weight, length and width were reduced by a high p.a. temperature treatment (35/15°C) applied for 4-days or more from 6-days after anthesis (daa). In addition, endosperm cell number and size were significantly reduced by a similar high p.a. temperature treatment duration applied from 6daa. Normal cell wall HG methyl-esterification status and distribution in the grain during development appeared to be accelerated by high p.a. temperatures suggesting a potential loss of cell wall plasticity in the pericarp and endosperm. RNA-Seq of high p.a. temperature treated grains revealed down-regulation of genes involved in cell wall expansion, including endoglucanase and β-expansin genes in the outer-pericarp at 10 and 14daa, coinciding with the early stabilisation of maximum grain moisture content, height and length in high p.a. temperature treated samples; traits closely associated with the pericarp during development. These results lend support to the overall hypothesis and help elucidate the interaction between grain layers under high p.a. temperatures, which may help molecular biologists and plant breeders develop more climate resilient cultivars.