Evolutional analysis of heat shock transcription factors in wild and cultivated rice (Oryza sativa L.)

Abstract Background：Heat shock transcription factors (Hsfs) take part in many physiological and biochemical pathways in plants by regulating the expression of various stress-responsive genes, such as heat shock proteins (Hsps). With the development of rice genome re-sequencing projects, some researches had been carried out to identify Hsf gene family members in rice at the whole genomic scale. However, Hsfs in cultivated and wild rice genomes has not been fully studied and compared, although genetic diversity in cultivated rice is limited compared to wild rice. Results：In this research work, Hsfs genes were screened and evolutionally compared in the genomes of 6 wild rice and 1 cultivated rice varieties, including O. barthii, O. glumaepatula, O. meridionalis, O. nivara, O. punctate, O. rufipogon and O. sativa & Nipponbare. Total 22, 23, 24, 24, 25, 25 and 25 Hsf genes were identified in the tested 7 rice genomes, respectively. The different number of Hsf genes between wild and cultivated rice genotypes was due to dispersed duplication and whole genome duplication (WGD) events, reversely contributed to different stress-tolerant ability between wild and cultivated rice. The evolutional analysis on the Hsf genes confirmed that O. rufipogon was the immediate ancestral progenitors of O. sativa. The expression profile of Hsf genes in Nipponbare and O. rufipogon under different stage of salinity stress showed that 4 root Hsf genes, including HsfA3a, HsfA4d, HsfC2a and HsfC2b, were simultaneously up-regulated by salinity stress in cultivated rice and its ancestral progenitor, implying that these 4 Hsf genes played conserved roles in rice in response to salinity stress. However, a substantial number of Hsf genes were exclusively regulated only in Oryza rufipogon rice seedling, suggesting that some of genuine salinity stress tolerance genes might be missing in cultivated rice. Conclusion：The results of this study would give insight into the evolution and function of Hsf gene members in rice, and hint to the use of wild relative genes to improve rice performance.