Pi (inorganic phosphate) limitation severely impairs plant growth and reduces crop yield. Hence plants have evolved several biochemical and morphological responses to Pi starvation that both enhance uptake and conserve use. The mechanisms involved in Pi sensing and signal transduction are not completely understood. In the present study we report that a previously uncharacterized transcription factor, BHLH32, acts as a negative regulator of a range of Pi starvation-induced processes in Arabidopsis. In bhlh32 mutant plants in Pi-sufficient conditions, expression of several Pi starvation-induced genes, formation of anthocyanins, total Pi content and root hair formation were all significantly increased compared with the wild-type. Among the genes negatively regulated by BHLH32 are those encoding PPCK (phosphoenolpyruvate carboxylase kinase), which is involved in modifying metabolism so that Pi is spared. The present study has shown that PPCK genes are rapidly induced by Pi starvation leading to increased phosphorylation of phosphoenolpyruvate carboxylase. Furthermore, several Arabidopsis proteins that regulate epidermal cell differentiation [TTG1 (TRANSPARENT TESTA GLABRA1), GL3 (GLABRA3) and EGL3 (ENHANCER OF GL3)] positively regulate PPCK gene expression in response to Pi starvation. BHLH32 can physically interact with TTG1 and GL3. We propose that BHLH32 interferes with the function of TTG1-containing complexes and thereby affects several biochemical and morphological processes that respond to Pi availability.

You do not currently have access to this content.