The relationship between cuticular lipids and associated gene expression in above ground organs of Thellungiella salsugineum (Pall.) Al-Shehbaz & Warwick

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 Salicornia europaea. 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 SeFAR1, SeFAR2, and SeFAR3 are implied to synthesize primary alcohols, and SeWSs convert the primary alcohols to wax esters; SeCER1 and SeCER3 are also supposed to catalyze the conversion of aldehydes to alkanes while SeMAH7 catalyze alkanes to secondary alcohols in S. europaea 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.

Chemical and Transcriptomic Analyses of Leaf Cuticular Wax Metabolism in Ammopiptanthus mongolicus under Osmotic Stress

Plant cuticular wax forms a hydrophobic structure in the cuticle layer covering epidermis as the first barrier between plants and environments. Ammopiptanthus mongolicus, a leguminous desert shrub, exhibits high tolerances to multiple abiotic stress. The physiological, chemical, and transcriptomic analyses of epidermal permeability, cuticular wax metabolism and related gene expression profiles under osmotic stress in A. mongolicus leaves were performed. Physiological analyses revealed decreased leaf epidermal permeability under osmotic stress. Chemical analyses revealed saturated straight-chain alkanes as major components of leaf cuticular wax, and under osmotic stress, the contents of total wax and multiple alkane components significantly increased. Transcriptome analyses revealed the up-regulation of genes involved in biosynthesis of very-long-chain fatty acids and alkanes and wax transportation under osmotic stress. Weighted gene co-expression network analysis identified 17 modules and 6 hub genes related to wax accumulation, including 5 enzyme genes coding KCS, KCR, WAX2, FAR, and LACS, and an ABCG transporter gene. Our findings indicated that the leaf epidermal permeability of A. mongolicus decreased under osmotic stress to inhibit water loss via regulating the expression of wax-related enzyme and transporter genes, further promoting cuticular wax accumulation. This study provided new evidence for understanding the roles of cuticle lipids in abiotic stress tolerance of desert plants.

The COPII subunit CsSEC23 mediates fruit glossiness in cucumber

To improve our understanding of the mechanism underlying cucumber glossiness regulation, a novel cucumber mutant with a glossy peel (Csgp) was identified. MutMap, genotyping, and gene editing results demonstrated that CsSEC23, which is the core component of COPII vesicles, mediates the glossiness of cucumber fruit peel. CsSEC23 is functionally conserved and located in the Golgi and endoplasmic reticulum. CsSEC23 could interact with CsSEC31, but this interaction was absent in the Csgp mutant, which decreased the efficiency of COPII vesicle transportation. Genes related to wax and cutin transport were upregulated in the Csgp mutant, and the cuticle structure of the Csgp-mutant peel became thinner. Moreover, the wax and cutin contents were also changed due to CsSEC23 mutation. Taken together, the results obtained from this study revealed that CsSEC23 mediates cucumber glossiness, and this mediating might be affected by COPII vesicle transportation.

Cuticular lipids and associated gene expression analysis under NaCl stress in Thellungiella salsuginea

Cuticular lipids, including wax and cutin, protect plants against external environmental stress. The relationship between the cuticle properties and salt tolerance is not clear. In this article, photosynthetic and physiological characteristics related to water use and cuticle permeability were assessed in the leaves of Thellungiella salsuginea under NaCl stress. The chemical composition of wax and cutin monomers, and the expression of cuticle-associated genes were also analyzed. The results showed that the net photosynthetic rate and stomatal conductance in the leaves of T. salsuginea decreased, and the water use efficiency increased with increasing NaCl concentration. Salt stress caused a significant increase in total wax, but total cutin monomers only increased under high salt. Transcriptome sequencing and lipid metabolism pathway analysis were performed on rosette leaves of T. salsuginea after 24 h of NaCl treatment. We analyzed the expression of 42 genes involved in cuticle lipid metabolism, and found that most of them exhibited higher expression levels at 0.15 mol L^-1 NaCl, but lower expression levels at 0.3 mol L^-1 NaCl. The expression of 12 of these genes was further detected by qRT-PCR after 1 week of NaCl treatment: most of them were upregulated both under low and high NaCl stress. Hence, we speculate that the cuticle acts as an adaptive trait in T. salsuginea in salty environments.