Lack of Purple Acid Phosphatase SlPAP26b compromises the phosphorous starvation response in tomato independent of SlPHR1 and SlPHL1

The scarcity of soil phosphorus (P), an essential macronutrient, often limits plant growth and development. Enhanced secretion of intracellular and secretory acid phosphatases is essential to maintain cellular inorganic P (Pi) homeostasis in plants. Herein, using transcriptomics and proteomics approach, we observed upregulation of several purple acid phosphatases (PAPs), including SlPAP1, SlPAP10b, SlPAP12, SlPAP15, SlPAP17b, SlPAP26a, and SlPAP26b in Pi-deficient tomato seedlings. Higher transcript levels of SlPAP17b and SlPAP26b in the older senescing leaves than the younger leaves indicated active involvement of these PAPs in Pi remobilization. Subsequent detailed characterization of SlPAP17b, SlPAP26a, and SlPAP26b revealed a prominent role of SlPAP26b in Pi homeostasis. Silencing of SlPAP26b led to an exacerbated P starvation response as these plants exhibited smaller shoots, lower soluble Pi, total P levels, and higher sucrose than their EV controls under Pi deprivation. SlPAP26b-silenced plants also showed misregulation of P starvation inducible genes such as phosphate transporters and glycerolipid remodellers, even under Pi-sufficient conditions. Whereas SlPAP26b levels were induced by external sucrose, its expression was found to be independent of the Myb class master regulators of P starvation response, SlPHR1 and SlPHL1. Altogether, this study identifies a prominent role of SlPAP26b in the Pi compensation network in tomato seedlings.