Allelic variation in rice fertilization independent endosperm 1 contributes to grain width under high night temperature stress

Authors: DHATT, BALPREET - University Of Nebraska; PAUL, PUNEET - University Of Nebraska; SANDHU, JASPREET - University Of Nebraska; HUSSAIN, WASEEM - International Rice Research Institute; IVIN, LARISSA - University Of Nebraska; ZHU, FEIYU - University Of Nebraska; Adviento-Borbe, Arlene; LORENCE, ARGELIA - Arkansas State University; STASWICK, PAUL - University Of Nebraska; YU, HONGFENG - University Of Nebraska; MORATA, GOTA - Virginia Polytechnic Institution & State University; HARKAMAL, WALIA - University Of Nebraska

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/9/2020
Publication Date: 8/20/2020
Citation: Dhatt, B., Paul, P., Sandhu, J., Hussain, W., Ivin, L., Zhu, F., Adviento-Borbe, A.A., Lorence, A., Staswick, P., Yu, H., Morata, G., Harkamal, W. 2020. Allelic variation in rice fertilization independent endosperm 1 contributes to grain width under high night temperature stress. New Phytologist. 229(1)/335-350. https://doi.org/10.1111/nph.16897.
DOI: https://doi.org/10.1111/nph.16897

Interpretive Summary: The global mean surface air temperature has increased by ~0.5oC in the last century. Rice which is a stable food and a major source of human calories, is highly sensitive to minimum air temperature increase. Field studies indicate a nearly 10% decline in grain yield for every 10oC increment increase in minimum air temperature. It is projected that a large increase in air temperature will have a huge impact on rice yield. Grain weight, size, and width are metrics of grain yield. Currently, genetic studies of the architecture of rice have identified genes regulating rice grain size under optimal growing condition. However, the genes regulating grain size under high night air temperature (HNT) have not been determined. Using 173 rice accessions and a gene mapping study called genemo-wide association (GWA), we identified two HNT-specific locus, Os12g40930 and Os12g40940, that were associated with rice grain length and genetic marker (single nucleotide polymorphism – SNP) chr8.2098482 closed to four genes (Os08g37980, Os08g37990, Os08g38000, and Os08g38010) were strongly associated with grain width trait under HNT. This gene is restricted to protein region of Fertilization Independent Endosperm 1 (Fiel1) which encodes for Polycomb Repressive Complex 2 protein (PRC2). PRC2 is involved in the grain development of rice plant. These gene discoveries will significantly improve understanding of rice adaptation to heat stress and enable efforts for breeding temperature-resilient rice varieties.

Technical Abstract: A higher minimum (nighttime) temperature is considered a greater limiting factor for reduced rice yield than a similar increase in maximum (daytime) temperature. While the physiological impact of high night temperature (HNT) has been studied, the genetic and molecular basis of HNT stress response remains unexplored. We examined the phenotypic variation for mature grain size (length and width) in a diverse set of rice accessions under HNT stress. Genome-wide association analysis identified several HNT-specific loci regulating grain size as well as loci that are common for optimal and HNT stress conditions. A novel locus contributing to grain width under HNT conditions co-localized with Fie1, a component of the FIS-PRC2 complex. Our results suggest that the allelic difference controlling grain width under HNT is due to differential transcript level response of Fie1 in grains developing under HNT stress. We present evidence to support the role of Fie1 in grain size regulation by testing overexpression (OE) and knock-out mutants under heat stress. The OE mutants were either unaltered or had a positive impact on mature grain size under HNT, while the knockouts exhibited significant grain size reduction under these conditions.