Stress- and phospholipid signalling responses in Arabidopsis PLC4-KO and -overexpression lines under salt- and osmotic stress

Several drought- and salt tolerant phenotypes have been reported when overexpressing (OE) phospholipase C (PLC) genes across plant species. In contrast, a negative role for Arabidopsis PLC4 in salinity stress was recently proposed by Xia et al., (2017) since they reported roots of PLC4-OE seedlings to be were more sensitive to NaCl while plc4-KO mutants were more tolerant. To investigate this apparent contradiction, and to analyse the phospholipid signalling responses associated with salt stress, we performed root growth- and phospholipid analyses on plc4-KO and PLC4-OE seedlings subjected to salinity (NaCl) or osmotic (sorbitol) stress, and compared these to wild type (WT) plants. Only very minor differences between PLC4 mutants and WT were observed, which even disappeared after normalization of the data, while in soil, PLC4-OE plants were clearly more drought tolerant than WT plants, as was found earlier when overexpressing Arabidopisis PLC2, -3, -5, -7 or -9. We conclude that PLC4 plays no opposite role in salt-or osmotic stress and rather behaves like the other Arabidopsis PLCs.