Specific galactolipids species correlate with rice genotypic variability for phosphate utilization efficiency

Lipidome Profiling of Phosphorus Deficiency-Tolerant Rice Cultivars Reveals Remodeling of Membrane Lipids as a Mechanism of Low P Tolerance

Plants have evolved various mechanisms for low P tolerance, one of which is changing their membrane lipid composition by remodeling phospholipids with non-phospholipids. The objective of this study was to investigate the remodeling of membrane lipids among rice cultivars under P deficiency. Rice (Oryza sativa L.) cultivars (Akamai, Kiyonishiki, Akitakomachi, Norin No. 1, Hiyadateine, Koshihikari, and Netaro) were grown in 0 (-P) and 8 (+P) mg P L^-1 solution cultures. Shoots and roots were collected 5 and 10 days after transplanting (DAT) in solution culture and subjected to lipidome profiling using liquid chromatography-mass spectrometry. Phosphatidylcholine (PC)34, PC36, phosphatidylethanolamine (PE)34, PE36, phosphatidylglycerol (PG)34, phosphatidylinositol (PI)34 were the major phospholipids and digalactosyldiacylglycerol (DGDG)34, DGDG36, 1,2-diacyl-3-O-alpha-glucuronosylglycerol (GlcADG)34, GlcADG36, monogalactosyldiacylglycerol (MGDG)34, MGDG36, sulfoquinovosyldiacylglycerol (SQDG)34 and SQDG36 were the major non-phospholipids. Phospholipids were lower in the plants that were grown under -P conditions than that in the plants that were grown under +P for all cultivars at 5 and 10 DAT. The levels of non-phospholipids were higher in -P plants than that in +P plants of all cultivars at 5 and 10 DAT. Decomposition of phospholipids in roots at 5 DAT correlated with low P tolerance. These results suggest that rice cultivars remodel membrane lipids under P deficiency, and the ability of remodeling partly contributes to low P tolerance.

Advances in Plant Lipid Metabolism Responses to Phosphate Scarcity

Low phosphate (Pi) availability in soils severely limits crop growth and production. Plants have evolved to have numerous physiological and molecular adaptive mechanisms to cope with Pi starvation. The release of Pi from membrane phospholipids is considered to improve plant phosphorus (P) utilization efficiency in response to Pi starvation and accompanies membrane lipid remodeling. In this review, we summarize recent discoveries related to this topic and the molecular basis of membrane phospholipid alteration and triacylglycerol metabolism in response to Pi depletion in plants at different subcellular levels. These findings will help to further elucidate the molecular mechanisms underlying plant adaptation to Pi starvation and thus help to develop crop cultivars with high P utilization efficiency.

Monogalactosyl diacylglycerol synthase 3 affects phosphate utilization and acquisition in rice

Galactolipids are essential to compensate for the loss of phospholipids by 'membrane lipid remodelling' in plants under phosphorus (P) deficiency conditions. Monogalactosyl diacylglycerol (MGDG) synthases catalyse the synthesis of MGDG which is further converted into digalactosyl diacylglycerol (DGDG), later replacing phospholipids in the extraplastidial membranes. However, the roles of these enzymes are not well explored in rice. In this study, the rice MGDG synthase 3 gene (OsMGD3) was identified and functionally characterized. We showed that the plant phosphate (Pi) status and the transcription factor PHOSPHATE STARVATION RESPONSE 2 (OsPHR2) are involved in the transcriptional regulation of OsMGD3. CRISPR/Cas9 knockout and overexpression lines of OsMGD3 were generated to explore its potential role in rice adaptation to Pi deficiency. Compared with the wild type, OsMGD3 knockout lines displayed a reduced Pi acquisition and utilization while overexpression lines showed an enhancement of the same. Further, OsMGD3 showed a predominant role in roots, altering lateral root growth. Our comprehensive lipidomic analysis revealed a role of OsMGD3 in membrane lipid remodelling, in addition to a role in regulating diacylglycerol and phosphatidic acid contents that affected the expression of Pi transporters. Our study highlights the role of OsMGD3 in affecting both internal P utilization and P acquisition in rice.