Functional identification of two Glycerol-3-phosphate Acyltransferase5 homologs from Chenopodium quinoa

Glycerol-3-phosphate acyltransferase5 (GPAT5) is the key enzyme in suberin biosynthesis in Arabidopsis, tomato and Sarracenia purpurea. However, little is known about whether GPAT5 function is conserved in halophytes. In this study, we identified two GPAT5 homologs, CqGPAT5a and CqGPAT5b, in Chenopodium quinoa, the typical halophyte. Using RT-qPCR, we found that CqGPAT5a and CqGPAT5b were highly expressed in quinoa roots and rapidly induced by high salt stress. CqGPAT5a and CqGPAT5b were localized to the endoplasmic reticulum and found to have glycerol-3-phosphate acyltransferase activity using yeast complementation assays. Compared with CqGPAT5b, CqGPAT5a showed relatively weaker function and less protein abundance when expressed in yeast, Arabidopsis or Nicotiana benthamiana. Subsequently, we identified a serine (S) to leucine (L) variation in the CqGPAT5a protein sequence (S251L) compared with CqGPAT5b, located in the connecting region between the second and third transmembrane domains. Site-directed mutagenesis together with yeast mutant complementation and transient expression in tobacco demonstrated that this variation significantly affected CqGPAT5a activity and protein abundance. These findings expand our understanding of GPAT5 and provide new evidence that GPAT5 may be functionally conserved in halophytes.