Wetting alternated moderate drying promotes phosphorus uptake and transport by regulating levels of brassinosteroids and jasmonates in rice

The purpose of this study was to investigate whether and how brassinosteroids (BRs) and jasmonates (JAs) respond to irrigation regimes and mediate phosphorus (P) uptake and transport in rice. Over three years, an Indica/Japonica rice cultivar was grown in the field at either no P fertilizer application (0 P) or with P fertilizer application (NP). Three irrigation regimes were implemented: continuously flooding (CF), wetting alternated with moderate drying (WMD), and wetting alternated with severe drying (WSD). The results showed that, compared to CF and at both 0 P and NP, WMD significantly increased BRs levels in roots and leaves and JAs levels in leaves, leading to increases in acid phosphatase (APase) activities in roots and proton-pumping ATPase (H⁺-ATPase) activities and the expression of genes related to P uptake and transport in both roots and leaves, P uptake and transport, grain yield, irrigation water productivity, and internal P use efficiency (PIE). WSD decreased BRs levels in plants, APase activities and the gene expression in roots, P uptake, and grain yield. However, WSD substantially enhanced JAs levels in roots and leaves, and increased H⁺-ATPase activities and the gene expression in leaves and ribonuclease activities in both roots and leaves, P transport from straws to the grain, resulting in an increase of PIE. Applying 24-epibrassinolide and jasmonic acid verified roles of BRs and JAs in regulating P uptake and transport. These findings suggest that elevating BRs levels in both roots and leaves and JAs levels in leaves is an important strategy to increase grain yield and PIE, and WMD is an effective way to realize the strategy.