How does post-flowering heat impact grain growth and its determining processes in wheat?

Wheat grain yield is anticipated to suffer from the increased temperatures expected under climate change. In particular, the effects of post-anthesis temperatures on grain growth and development must be better understood to improve crop models. Grain growth and development involve several processes and we hypothesized that some of the most important processes, i.e. grain dry biomass and water accumulation, grain volume expansion and endosperm cell proliferation, will have different thermal sensitivity. To assess this, we established temperature response curves (TRC) of these processes for steady post-anthesis temperatures between 15°C and 36°C. From anthesis to maturity, grain dry mass, water mass, volume and endosperm cell number were monitored, whilst considering grain temperature. Different sensitivities to heat of these various processes were revealed. The rate of grain dry biomass accumulation increased linearly up to 25°C while the reciprocal of its duration linearly increased up to at least 32°C. By contrast, the growth rates of traits contributing to grain expansion, e.g. increase in grain volume and cell numbers, had higher optimum temperatures, while the reciprocal of their durations were significantly lower. These TRC can contribute to improve current crop models, and allow to target specific mechanisms for genetic and genomic studies.