The involvement of abscisic acid-insensitive mutants in low phosphate stress responses during rhizosphere acidification, anthocyanin accumulation and Pi homeostasis in Arabidopsis

Phosphorus is an essential plant nutrient, used in the formation of macromolecules such as nucleic acids and phospholipids. Abscisic acid (ABA) may be involved in the process of low inorganic phosphate (Pi) responses. The phenotypes of ABA-insensitive Arabidopsis mutants (abi1/2/3/4/5) under low Pi stress were investigated to identify possible low Pi response mutant genes. The results showed enhanced rhizosphere acidification in the abi1-1/abi2-1/abi5-1 mutants under low Pi stress compared with wild-type (WT) seedlings. The abi1-1/abi2-1/ abi3-1/abi5-1 mutants accumulated less anthocyanin than the WT, while the abi4-1 mutant showed greater accumulation, implicating all the ABA-insensitive mutants in anthocyanin deposition under Pi deficiency. Alterations in the Pi contents of roots or shoots were also observed in the mutants in response to both Pi sufficiency and deficiency, indicating that the mutants were involved in Pi uptake or transportation. The primary root length and root-shoot ratio of abi3-1 and abi4-1 mutants decreased compared with WT seedlings under low Pi condition. Further research showed that ABI5 could regulate PHT1;5 and WRKY42 expression by combining with ACGT cis-acting elements of the PHT1;5 and WRKY42 promoters.