High temperature during grain filling induces transgenerational heat stress memory in rice (Oryza sativa L.)

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Seeds developed under high temperature showed significantly delayed germination compared to control under the same non-stressed condition. This delay in germination was due to transcriptional changes after imbibition caused by hyper-methylation of ABA catabolism genes, and α-amylase gene. Higher methylation levels of target genes were confirmed by both Chop-qPCR and MeDIP-qPCR, which showed similar results stating that hyper-methylation of ABA catabolism genes and of α-amylase genes was involved in delayed seed germination of heat stressed seeds.At natural condition, plants grown from heat stressed seeds developed more tillers together with reduced height during vegetative growth despite unchanged total biomass compared to control plants. At harvest, heat stressed plants showed higher total panicle per plant, resulting in higher total spikelet number resulting higher yield. Other yield components, spikelet per panicle, 1000-grain weight, harvest index and seed setting rate, remained unchanged.We observed that early flowering phenotype and changes in leaf morphology were not cultivar-specific traits, by observing other 22 Japonica rice cultivars. Cultivar differences show that heat stress during grain filling induces transgenerational memory to the progeny to some content depending on cultivars.