Regulatory Mechanism Of Phosphate Translocation And Acquisition By AtWRKY28and AtWRKY42in Arabidopsis Plants

WRKY proteins belong to a unique transcription factor family in higher plants, and are involved in response to biotic and abiotic stresses. WRKY transcription factors have the conserved WRKY motif which shows high binding affinity to the DNA sequence TGAC. Phosphorus (P) is an essential macronutrient required for nearly all physiological and metabolic processes. This work showed that WRKY28and WRKY42play important roles in Pi acquisition and translocation in Arabidopsis.During Pi starvation, the transcript level of WRKY28was intensely induced. WRKY28RNAi lines, similar to the phol mutant, had lower shoot Pi contents compared with wild-type plants under Pi-deficient condition; however under Pi-sufficient condition, there was no obvious difference between WRKY28RNAi lines and wild-type plants, indicating that WRKY28mainly functioned under low-Pi stress. qRT-PCR results showed that the PHOl expression was significantly repressed in WRKY28RNAi lines under low-Pi stress, and elevated in WRKY28-overexpressing lines. And electrophoretic mobility shift assay (EMSA) showed that WRKY28could bind to the PHOl promoter in vitro. All the data demonstrate that WRKY28plays an important role in Pi translocation by regulating PHOl expression.WRKY28RNAi lines had lower root Pi contents compared with wild-type plants under low-Pi stress. Whereas the WRKY28-overexpressing lines showed arsenate sensitive phenotypes and higher Pi uptake rate compared with wild-type seedlings. The expression of PHT1;4was enhanced in WRKY28-overexpressing lines and slightly repressed in the WRKY28RNAi lines under Pi sufficient condition, and the PHT1;4was significantly repressed in the WRKY28RNAi lines during Pi starvation. The expression of PHT1;1was similar among all genotypes under Pi-sufficient or Pi-deficient condition. These results demonstrate that WRKY28is involved in phosphate acquisition through regulating PHT1;4expression.Similar to WRKY28-overexpressing lines, WRKY42-overexpressing lines had higher root Pi contents compared with wild-type plants under Pi-sufficient condition. The transcript level of PHT1;1was elevated in the WRKY42-overexpressing lines, and WRKY42positively regulated PHT1;1expression in tobacco leaves. Chromatin immunoprecipitation assay (ChIP) and EMSA assays showed that WRKY42could bind to the PHT1;1promoter in vivo and in vitro. The results demonstrate that WRKY42modulates Pi uptake through regulating PHT1;1expression.