Molecular Mechanisms Underlying The Role Of The Transcription Factor RVE7 In Thermomorphogenesis In Arabidopsis

Plant growth and development are widely affected by environmental conditions.Plants grow fixedly and cannot move like animals to avoid the adverse environment.Plants sense the changing environment and transduce these signals to downstream transcription factors to regulate gene expression and trigger subsequent physiological response to adapt to the changing environment.In the context of global warming,understanding the molecular mechanism of how plants respond to rising ambient temperature is helpful to improve the adaptability of plants to the environment.In higher plants,mild-warm temperature induces morphological changes,including the rapid growth of hypocotyl and petiole,the increase of leaf hyponasty and accelerated flowering in a process known collectively as thermomorphogenesis.The helix–loop–helix transcription factor PHYTOCHROME-INTERACTING FACTOR 4(PIF4)has a fundamental role in thermomorphogenesis in Arabidopsis.PIF4 mediates thermomorphogenesis by virtue of its capacity to bind the promoters of genes involved in auxin biosynthesis and signal transduction.ELF3 together with ELF4 and LUX,assembles into an evening complex(EC)to regulate the circadian clock.EC complex inhibits hypocotyl elongation during thermomorphogenesis by regulating PIF4 gene expression and PIF4 activity.ELF3 in EC complex is considered as a direct thermal sensor,which reduces its inhibitory effect on PIF4 through liquid-liquid phase separation at warm tempetature.However,whether other members of EC are also involved in warm temperature response is still unclear.In this study,we found that RVE7 is an essential positive regulator in thermomorphogenesis.RVE7 represses the expression of ELF4 in EC complex,thus promoting hypocotyl growth at warm temperature.The transcription level of RVE7 is up-regulated at elevated ambient temperature than that at normal temperature;The protein level of RVE7 is also increased in response to warm temperatures.Phenotypic analysis showed that under normal growth temperature,the hypocotyl lengths of the rve7 mutants were similar to that of the wild plants,but,under elevated high temperature,the hypocotyl lengths of rve7 mutants were significantly shorter than that of the wild type plants.The hypocotyl lengths of the RVE7 overexpression plants were dramatically longer than that of the WT plants under warm temperature,but there was no difference between the two under normal temperature conditions.Subsequent mutant genetic analysis showed that PIF4 was epistatic to RVE7;In addition,the hypocotyl phenotype of RVE7-overexpression plants at high temperature was dependent on PIF4.And western blotting analysis showed that when the temperature increased,the protein accumulation of PIF4 in rve7 mutant plants was lower than that in WT,and the accumulation of PIF4 in RVE7 overexpression plants was higher than that in WT;Under normal growth temperature,there was little difference in PIF4 protein level among the above materials.Consistent with the protein accumulation of PIF4,under warmth the expression levels of PIF4 downstream genes YUC8、F-box、IAA19 and XTR in RVE7 overexpression plants were higher than those in the wild type,and the expression levels of F-box and XTR in rve7 mutant were lower than those in the wild type.In addition,the expression level of ELF4 in RVE7 overexpression plants was lower than that in wild type,and the expression level of ELF4 in rve7 mutant was higher than that in wild type under warmth.Further biochemical experiments showed that RVE7 could bind to the EE cis-element presented in the ELF4 promoter and directly represses the expression of ELF4.Genetic analysis showed that ELF4 was epistatic to RVE7;The overexpression of ELF4 could inhibit the hypocotyl phenotype of RVE7 overexpression plants.Therefore,this paper identified RVE7 as an important regulatory factor of plant thermal morphogenesis.RVE7 mainly maintained the expression level of ELF4 by directly and negatively regulating the expression of ELF4.These studies clarified the molecular mechanism of RVE7 regulating downstream gene expression and deepen our understanding of the importance of ELF4 in plant thermomorphogenesis.