Binding affinities and interactions among different heat shock element types and heat shock factors in rice (Oryza sativa L.)

Binding of heat shock factors (Hsfs) to heat shock elements (HSEs) leads to transcriptional regulation of heat shock genes. Genome-wide, 953 rice genes contain perfect-type, 695 genes gap-type and 1584 genes step-type HSE sequences in their 1-kb promoter region. The rice genome contains 13 class A, eight class B and four class C Hsfs (OsHsfs) and has OsHsf26 (which is of variant type) genes. Chemical cross-linking analysis of in vitro synthesized OsHsf polypeptides showed formation of homotrimers of OsHsfA2c, OsHsfA9 and OsHsfB4b proteins. Binding analysis of polypeptides with oligonucleotide probes containing perfect-, gap-, and step-type HSE sequences showed that OsHsfA2c, OsHsfA9 and OsHsfB4b differentially recognize various model HSEs as a function of varying reaction temperatures. The homomeric form of OsHsfA2c and OsHsfB4b proteins was further noted by the bimolecular fluorescence complementation approach in onion epidermal cells. In yeast two-hybrid assays, OsHsfB4b showed homomeric interaction as well as distinct heteromeric interactions with OsHsfA2a, OsHsfA7, OsHsfB4c and OsHsf26. Transactivation activity was noted in OsHsfA2c, OsHsfA2d, OsHsfA9, OsHsfC1a and OsHsfC1b in yeast cells. These differential patterns pertaining to binding with HSEs and protein–protein interactions may have a bearing on the cellular functioning of OsHsfs under a range of different physiological and environmental conditions. Structured digital abstract •  HSFA2C binds to HSFA2C by cross-linking study (View interaction) •  HSFA2Cphysically interacts with HSFA2C by bimolecular fluorescence complementation(View interaction) •  HSFB4B physically interacts with HSFB4B by bimolecular fluorescence complementation(View interaction) •  HSFA2A physically interacts with HSFB4B by two hybrid (View interaction) •  HSFB4B binds to HSFB4B by cross-linking study (View interaction) •  HSFB4B physically interacts with HSF26 by two hybrid (View interaction) •  HSFA9 binds to HSFA9 by cross-linking study (View interaction) •  HSFA7 physically interacts with HSFB4B by two hybrid (View interaction) •  HSFB4B physically interacts with HSFB4C by two hybrid (View interaction) •  HSFB4B physically interacts with HSFB4B by two hybrid (View interaction)