WRKY42 Modulates Phosphate Homeostasis through Regulating Phosphate Translocation and Acquisition in Arabidopsis  

Abstract

The Arabidopsis (Arabidopsis thaliana) WRKY transcription factor family has more than 70 members, and some of them have been reported to play important roles in plant response to biotic and abiotic stresses. This study shows that WRKY42 regulated phosphate homeostasis in Arabidopsis. The WRKY42-overexpressing lines, similar to the phosphate1 (pho1) mutant, were more sensitive to low-inorganic phosphate (Pi) stress and had lower shoot Pi content compared with wild-type plants. The PHO1 expression was repressed in WRKY42-overexpressing lines and enhanced in the wrky42 wrky6 double mutant. The WRKY42 protein bound to the PHO1 promoter under Pi-sufficient condition, and this binding was abrogated during Pi starvation. These data indicate that WRKY42 modulated Pi translocation by regulating PHO1 expression. Furthermore, overexpression of WRKY42 increased root Pi content and Pi uptake, whereas the wrky42 mutant had lower root Pi content and Pi uptake rate compared with wild-type plants. Under Pi-sufficient condition, WRKY42 positively regulated PHOSPHATE TRANSPORTER1;1 (PHT1;1) expression by binding to the PHT1;1 promoter, and this binding was abolished by low-Pi stress. During Pi starvation, the WRKY42 protein was degraded through the 26S proteasome pathway. Our results showed that AtWRKY42 modulated Pi homeostasis by regulating the expression of PHO1 and PHT1;1 to adapt to environmental changes in Pi availability.Phosphorus is an essential nutrient for plant growth (Raghothama, 1999) and the main component of fertilizers to sustain modern agriculture. Approximately 70% of global cultivated land suffers from phosphate deficiency (López-Arredondo et al., 2014). Maintenance of phosphate homeostasis in plants is important for plant growth and reproduction, and it is achieved mainly by coordination of acquisition of inorganic phosphate (Pi; orthophosphate) from the soil solution, translocation of Pi from roots to shoots, and remobilization of internal Pi (Poirier and Bucher, 2002).Pi is the only form of phosphorus that can be absorbed in plants (Chiou and Lin, 2011;López-Arredondo et al., 2014). Plants take up Pi from soil solution through phosphate transporters (PHTs) encoded by members of the PHT1 gene family. There are at least nine members (PHT1;1-PHT1;9) of the PHT1 family in Arabidopsis (Arabidopsis thaliana), and transcripts of PHT1;1 are the most abundant among nine PHT1 genes (Mudge et al., 2002). PHT1;1 and PHT1;4 play important roles in Pi uptake from soil. Under high-Pi condition, the pht1;1 mutants' uptake rate was only 59% to 66% of the wild type, and the Pi uptake rates of pht1;4 mutants increased slightly (Shin et al., 2004), indicating that PHT1;1 plays an important role in Pi uptake under Pisufficient condition. During Pi starvation, the expressions of PHT1;1 and PHT1;4 are significantly induced (Muchhal et al., 1996;Karthikeyan et al., 2002;Mudge et al., 2002;Shin et al., 2004), and overexpression of PHT1;1 increases Pi uptake in Arabidopsis . Several transcription factors have been reported to regulat...

Gene expression profiling of flax (Linum usitatissimum L.) under edaphic stress

“…It was shown that WRKY family genes are involved in tolerance to phosphate starvation in rice: overexpression of WRKY74 gene increase tolerance to phosphate starvation, while lines with low WRKY74 level were sensitive to this stress [33]. In Arabidopsis , WRKY42 regulates phosphate homeostasis: WRKY42 overexpressing lines were more sensitive to phosphate deficiency [34]. However, overexpression of WRKY45 in Arabidopsis increased phosphate uptake [35].…”

A WRKY Transcription Factor Regulates Fe Translocation under Fe Deficiency

“…Accumulating evidence reveals that WRKY genes are also involved in plant responses to nutrient deficiency or toxicity. For example, a number of WRKYs regulate phosphate uptake and translocation in Arabidopsis (Devaiah et al, 2007;Chen et al, 2009;Wang et al, 2014;Su et al, 2015). Interestingly, W-boxes, the DNA binding sites of WRKY proteins, are enriched in the promoters of many Fe deficiency-responsive genes .…”

“…Recently, accumulating evidence has demonstrated that WRKY transcription factors also take part in the responses to nutritional stresses. For example, some WRKYs (WRKY6/42/45/75) regulate phosphate starvation responses in Arabidopsis (Devaiah et al, 2007;Chen et al, 2009;Wang et al, 2014;Su et al, 2015). Meanwhile, WRKY6 is involved in the response to boron deficiency (Kasajima et al, 2010).…”

Fungal and Plant Tools for the Uptake of Nutrients in Arbuscular Mycorrhizas

“…Two conserved motifs were identified into AM-induced PT promoters, one of this is P1BS and the other one is named MYCS (mycorrhiza transcription factor binding sequence) and both are involved in the activation of AM-responsive PT genes (Chen et al, 2010). In Arabidopsis plants, four WRKY proteins have been reported to be involved in Pi starvation signaling pathway (Devaiah et al, 2007;Chen et al, 2009;Wang et al, 2014b;Su et al, 2015). WRKY42, WRKY45 and WRKY75 have been identified as positive regulators of PHT1;1 genes (Devaiah et al, 2007;Su et al, 2015).…”