Phosphorus remobilization from rice flag leaves during grain filling: an RNA‐seq study

Abstract

SummaryThe physiology and molecular regulation of phosphorus (P) remobilization from vegetative tissues to grains during grain filling is poorly understood, despite the pivotal role it plays in the global P cycle. To test the hypothesis that a subset of genes involved in the P starvation response are involved in remobilization of P from flag leaves to developing grains, we conducted an RNA‐seq analysis of rice flag leaves during the preremobilization phase (6 DAA) and when the leaves were acting as a P source (15 DAA). Several genes that respond to phosphate starvation, including three purple acid phosphatases (OsPAP3, OsPAP9b and OsPAP10a), were significantly up‐regulated at 15 DAA, consistent with a role in remobilization of P from flag leaves during grain filling. A number of genes that have not been implicated in the phosphate starvation response, OsPAP26, SPX‐MFS1 (a putative P transporter) and SPX‐MFS2, also showed expression profiles consistent with involvement in P remobilization from senescing flag leaves. Metabolic pathway analysis using the KEGG system suggested plastid membrane lipid synthesis is a critical process during the P remobilization phase. In particular, the up‐regulation of OsPLDz2 and OsSQD2 at 15 DAA suggested phospholipids were being degraded and replaced by other lipids to enable continued cellular function while liberating P for export to developing grains. Three genes associated with RNA degradation that have not previously been implicated in the P starvation response also showed expression profiles consistent with a role in P mobilization from senescing flag leaves.

Molecular mechanisms underpinning phosphorus‐use efficiency in rice

“…The replacement of membrane phospholipids by lipids that do not contain P (membrane lipid remodelling) is a major response to Pi starvation and has been demonstrated in many plant species including cultivated crops (Plaxton & Tran, ; Tjellström, Andersson, Larsson, & Sandelius, ). Detailed discoveries of molecular and genetic regulation of lipid remodelling in rice are available from Mehra, Pandey, and Giri (), Mehra and Giri (), and Jeong et al (). The lipid remodelling pathway comprises several steps, and the initial step is the hydrolysis of phospholipids to yield diacylglycerol (DAG) and free Pi, which can then be remobilized to other organs (Figure ).…”

“…Phospholipid hydrolysis occurs either in a one‐step reaction catalysed by phospholipase C (PLC) or in a two‐step reaction catalysed by phospholipase D (PLD) and phosphatidate phosphatase (PAH; Nakamura, ). In response to Pi deficiency, PLC , PLD , and PAH genes are upregulated in rice (Table , Jeong et al, ; Mehra & Giri, ; Mehra et al, ). The function of PLC is to hydrolyse phospholipids resulting in DAG and a phosphorylated head group, which is then further hydrolysed by acid phosphatase (APase) to release Pi (Stigter & Plaxton, ).…”

A novel glycerophosphodiester phosphodiesterase improves phosphate deficiency tolerance in rice

“…Consistent with these observations, expression analysis of OsGDPD2 by qRT‐PCR also confirmed high expression of OsGDPD2 in the root, seed, and anthers (Figure S3). Interestingly, in a recent study, OsGDPD2 was also predicted to be involved in seed Pi loading by remobilization of Pi from senescing flag leaves (Jeong et al, ). Moreover, AtGDPD2 , the closest Arabidopsis homolog of OsGDPD2 (Figure S1), also showed very high expression in roots, flower, and silique (Cheng, Zhou, et al, ).…”

Can natural variation in grain P concentrations be exploited in rice breeding to lower fertilizer requirements?

“…These findings together with the poor association of PHI with grain P concentrations imply that breeding strategies aimed at reducing grain P concentrations will have to address the high rate of late P uptake possibly common in rice [10, 30], rather than focusing chiefly on re-translocation [31]. If targeting a reduction in late P uptake is not an acceptable strategy, one may have to find ways to deviate the late influx of P away from the panicle.…”