Comprehensive expression of various genes involved in storage protein synthesis in filling rice grain as affected by high temperature

High temperature (HT) at the filling stage is a major environmental constraint to rice (Oryza sativa L.) grain quality. However, the effects of HT on the accumulation and composition of storage proteins are not well understood. In this study, the transcriptional expressions of genes related to storage protein synthesis responsive to HT, and their relationship with storage protein composition, were comprehensively analyzed under controlled temperature using two non-waxy indica rice cultivars, 9311 and II-7954. HT reduced grain weight and increased total protein content (TPC) irrespective of rice genotype, and HT-inducible increase in TPC was attributable to the relative increase in proportion of the aleurone fraction to whole grain, as well as increased absolute amount of TPC in rice grain; HT resulted in a relatively higher ratio of glutelin to prolamin compared with the control temperature, as reflected by a significant decrease in amount of 13-kDa prolamin polypeptide and an enhanced accumulation of proglutelin, alpha-glutelin and beta-glutelin subunits throughout the whole grain filling; The remarkably lowering of transcripts of glutelin and/or prolamin family genes in HT-ripening grain at the middle and late filling stage possibly were closely associated with the repressing regulation of RPBF induced by HT, while RISBZ1 was possibly mainly responsible for regulating the response of glutelin family genes to HT at the earlier filling stage. In addition, HT accelerated expressions of PDI and BiP to assist with the proper folding and assembly of proglutelin.