Maize Inositol Polyphosphate 5-phosphatase Gene Family Analysis Reveals Zm5PTase25 as a Negative Regulator of Low Phosphate-Induced Leaf Senescence.

Phosphate (Pi) deficiency promotes premature leaf senescence in plants through complex molecular networks; however, the underlying mechanisms remain poorly understood. Inositol polyphosphate 5-phosphatases (5PTases) are key regulators of inositol phosphate metabolism, but the maize (Zea mays L.) 5PTase gene family and its roles in low Pi (LP)-induced leaf senescence have not been systematically investigated. Here, we identified 31 members of the Zm5PTase family in the maize genome. Phylogenetic and structural analyses revealed marked divergence among clades. Among these genes, Zm5PTase25 was preferentially expressed in senescing leaves and significantly downregulated under LP stress. Functional analyses indicated that Zm5PTase25 negatively regulates LP-induced leaf senescence. Silencing Zm5PTase25 accelerated leaf senescence, promoted anthocyanin accumulation, altered Pi distribution between old and young leaves in a manner consistent with enhanced Pi remobilisation, and upregulated senescence- and ribonuclease-associated genes and repressed photosynthesis-related genes. Conversely, overexpression of Zm5PTase25 delayed leaf senescence. In vitro assays showed that Zm5PTase25 bound and hydrolysed soluble InsP3 and InsP4. The PHR1-like transcription factor ZmPHL6 was identified as a potential upstream transcriptional repressor of Zm5PTase25. Moreover, silencing ZmPHL6 produced phenotypes opposite to those of Zm5PTase25-silenced plants. Collectively, our findings suggest that the ZmPHL6-Zm5PTase25 regulatory module may modulate LP-induced leaf senescence, potentially by influencing source to sink Pi remobilisation, providing insights into molecular mechanisms coordinating leaf senescence with maize adaptation to Pi starvation.