Abscisic acid facilitates phosphate acquisition through the transcription factor ABA INSENSITIVE5 in Arabidopsis

SUMMARY Low phosphate (LP) in soil is a common nutrient stress that severely restricts agricultural production, but the role, if any, of the major stress phytohormone abscisic acid (ABA) in plant phosphate (Pi) starvation responses remains elusive. Here, we report that LP‐induced ABA accumulation promotes Pi uptake in an ABA INSENSITIVE5 (ABI5)‐dependent manner in Arabidopsis thaliana. LP significantly activated plant ABA biosynthesis, metabolism, and stress responses, suggesting a role of ABA in the plant response to Pi availability. LP‐induced ABA accumulation and expression of two major high‐affinity phosphate transporter genes PHOSPHATE TRANSPORTER1;1/1;4 (PHT1;1/1;4) were severely impaired in a mutant lacking BETA‐GLUCOSIDASE1 (BG1), which converts conjugated ABA to active ABA, and the mutant had shorter roots and less Pi content than wild‐type plants under LP conditions. Moreover, a mutant of ABI5, which encodes a central transcription factor in ABA signaling, also exhibited suppressed root elongation and had reduced Pi content under LP conditions. ABI5 facilitated Pi acquisition by activating the expression of PHT1;1 by directly binding to its promoter, while overexpression of PHT1;1 completely rescued its Pi content under LP conditions. Together, our findings illustrate a molecular mechanism by which ABA positively modulates phosphate acquisition through ABI5 in the Arabidopsis response to phosphate deficiency. Significance Statement Low phosphate (LP) is a common nutrient stress that severely suppresses plant growth and development, while whether and how the major stress phytohormone abscisic acid (ABA) functions in plant phosphate (Pi) starvation responses remains elusive. Our study showed that LP‐induced ABA promotes Pi uptake by activating PHOSPHATE TRANSPORTER1;1 expression in an ABA INSENSITIVE5‐dependent manner in Arabidopsis thaliana under LP.