The WRKY6 Transcription Factor ModulatesPHOSPHATE1Expression in Response to Low Pi Stress inArabidopsis

Yi-Fang Chen,Hui Wang,Li-Qin Li,Qian Xu,You-Han Kong,Wei-Hua Wu

doi:10.1105/tpc.108.064980

Yi-Fang Chen, Hui Wang + Show 4 more

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https://doi.org/10.1105/tpc.108.064980

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Abstract

Arabidopsis thaliana WRKY family comprises 74 members and some of them are involved in plant responses to biotic and abiotic stresses. This study demonstrated that WRKY6 is involved in Arabidopsis responses to low-Pi stress through regulating PHOSPHATE1 (PHO1) expression. WRKY6 overexpression lines, similar to the pho1 mutant, were more sensitive to low Pi stress and had lower Pi contents in shoots compared with wild-type seedlings and the wrky6-1 mutant. Immunoprecipitation assays demonstrated that WRKY6 can bind to two W-boxes of the PHO1 promoter. RNA gel blot and beta-glucuronidase activity assays showed that PHO1 expression was repressed in WRKY6-overexpressing lines and enhanced in the wrky6-1 mutant. Low Pi treatment reduced WRKY6 binding to the PHO1 promoter, which indicates that PHO1 regulation by WRKY6 is Pi dependent and that low Pi treatment may release inhibition of PHO1 expression. Protein gel blot analysis showed that the decrease in WRKY6 protein induced by low Pi treatment was inhibited by a 26S proteosome inhibitor, MG132, suggesting that low Pi-induced release of PHO1 repression may result from 26S proteosome-mediated proteolysis. In addition, WRKY42 also showed binding to W-boxes of the PHO1 promoter and repressed PHO1 expression. Our results demonstrate that WRKY6 and WRKY42 are involved in Arabidopsis responses to low Pi stress by regulation of PHO1 expression.

Highlights

Phosphorus (P), as a major essential nutrient for plant growth and development, serves various basic biological functions in the plant life cycle (Raghothama, 1999)
Under this low Pi stress condition, the 35S:WRKY6-9 line displayed thinner stalks and smaller leaves compared with wild-type plants (Figure 1A)
After wild-type plants were challenged with low Pi stress, WRKY6 expression level was increased during the first 3 h and decreased, but stayed above its zero time expression level for ;48 h. Another hypothesis we proposed was that the Pi starvation inhibits WRKY6 functioning in suppression of PHO1 expression, such as through a possible blockage of WRKY6 binding to W-box motifs of the PHO1 promoter or a low Pi–induced WRKY6 protein degradation

Summary

Introduction

Phosphorus (P), as a major essential nutrient for plant growth and development, serves various basic biological functions in the plant life cycle (Raghothama, 1999). The Pi concentration in the soil, typically 10 mM or less, results in Pi starvation for plant growth and survival, which is one of major limiting factors for crop production in the cultivated soils. In response to low Pi stress or Pi starvation, plants may increase the Pi uptake from the soil by alteration of root architecture and function (Lopez-Bucio et al, 2003; Ticconi and Abel, 2004; Osmont et al, 2007). Under Pi-limiting conditions, plants may increase their Pi acquisition by changing their metabolic and developmental processes (Raghothama and Karthikeyan, 2005), such as increasing phosphatase activity (Lipton et al, 1987) and secretion of organic acids (Marschner, 1995)

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