Identification and Analysis of Cuticular Wax Biosynthesis Related Genes in Salicornia europaea Under NaCl Treatment

Salinity is a major environmental factor that adversely affects plant growth and production. Cuticular wax protects plants against external environmental stress. The relationship between cuticular wax biosynthesis and salt tolerance remains unclear in <i>Salicornia europaea</i>. This study examined the cuticle thickness, wax load, morphology, composition, and the expression of cuticular wax biosynthesis gene identification and expression. The results showed that 600 mM NaCl treatment enhanced the cuticle thickness and total wax load; crystal wax structures were also observed after NaCl treatment. The cuticular wax was mainly composed of fatty acids, alcohols, alkenes, and esters. The alcohol class accounted for the largest proportion, with docosanol (C₂₅H₅₄OSi) being the main specific alcohol compound, followed by fatty acids and alkanes. After a sequence database search, six fatty acyl-CoA reductases (FARs), sixteen wax synthase/diacylglycerol acyltransferases (WS/DGATs), three fatty alcohol oxidases (FAOs), five eceriferums (CERs), and eight mid-chain alkanes (MAHs) were identified as the putative wax biosynthesis enzymes. Their expression analysis revealed a differential response to 100 and 600 mM NaCl treatment and reached the highest level at 12 h or 48 h. The genes that were evidently upregulated with higher fold changes under salinity, such as <i>SeFAR1</i>, <i>SeFAR2</i>, and <i>SeFAR3</i> are implied to synthesize primary alcohols, and <i>SeWSs</i> convert the primary alcohols to wax esters; <i>SeCER1</i> and <i>SeCER3</i> are also supposed to catalyze the conversion of aldehydes to alkanes while <i>SeMAH7</i> catalyze alkanes to secondary alcohols in <i>S. europaea</i> in response to NaCl treatment. This study demonstrated that both the decarbonylation and acyl-reduction wax biosynthesis pathways may not be independent from each other.