Experimental Evidence For Involvement Arabidopsis Transcription Factor AtHSFA6b In Response To Low Phosphorous Stress

Phosphorus is an essential nutrient for plant growth and development.The phosphate(Pi)concentration in the soil,typically 10 μM or less,results in Pi starvation for plant growth and survival.During Pi starvation,the expression of many genes significantly changed in plants,indicating that transcriptional regulation plays important roles in plant responses to low-Pi stress.Arabidopsis HSF transcription factor family has 21 members,and some of them have been reported to play roles in plant development and stress responses.The focus of this dissertation work is to study the potential function of transcription factor HSFA6b in plant responses to low-Pi stress.HSFA6b belongs to the A subfamily of HSF transcription factor family,and the HSFA6b:GFP fusion protein is localized in the nucleus.The HSFA6b can bind to HSE,the cis element bound by HSF proteins in vitro,and the HSFA6b also showed transcriptional activation activity in yeast,indicating that HSFA6b can function as a transcription factor.The HSFA6b is expressed in shoots and roots,and its expression was repressed under low-Pi condition.These data suggest that HSFA6b is a Pi-starvation-responsive transcription factor.To reveal the function of HSFA6b,the T-DNA insertion mutant of HSFA6b,named 6b-1,was obtained from ABRC.When grown on Pi-deficient condition,the 6b-1 mutant was more tolerant to low-Pi stress,and accumulated less anthocyanin content than wild-type plants.In addition,the 6b-1 mutant had higher Pi content and enhanced Pi uptake rate relative to wild-type plants.Two 6b1-1 complementation lines showed similar phenotypes and Pi contents with the wild-type plants under either Pi-sufficient or Pi-deficient condition,demonstrating that the phenotypes of 6b-1 mutant resulted from the disruption of HSFA6b.The HSFA6b-overexpressing lines displayed low-Pi sensitive phenotypes,and accumulated more anthocyanin contents compared with wild-type plants when grown on Pi-deficient condition.And the Pi contents and Pi uptake rates of HSFA6b-overexpressing lines were much lower than those of wild-type plants,indicating that overexpression of HSFA6b represses plant Pi acquisition.Under Pi-sufficient condition,the shoot/root Pi ratiosin 6b-1 mutant or HSFA6b-overexpressing lines were similar to that in wild-type plants,suggesting that HSFA6b might not modulate Pi translocation between root and shoot.To further test the mechanism of HSFA6b in modulating Pi uptake,the transcription of genes encoding Pi transporters or Pi uptake regulators were analyzed.Surprisingly,there was no significant difference among the 6b-1 mutant,HSFA6b-overexpressing lines and wild-type plants.Molecular mechanism of Pi uptake regulation by HSFA6b need to be further investigated.In summary,this dissertation work demonstrates that HSFA6b is a Pi-starvation-responsive transcription factor and it participates in plant response to low-Pi stress possibly by negatively modulating Pi uptake.