Genome-wide analysis of glycerol-3-phosphate O-acyltransferase gene family and functional characterization of two cutin group GPATs in Brassica napus

Genome-Wide Identification, Characterization, Evolutionary Analysis, and Expression Pattern of the GPAT Gene Family in Barley and Functional Analysis of HvGPAT18 under Abiotic Stress

Glycerol-3-phosphoacyltransferase (GPAT) is an important rate-limiting enzyme in the biosynthesis of triacylglycerol (TAG), which is of great significance for plant growth, development, and response to abiotic stress. Although the characteristics of GPAT have been studied in many model plants, little is known about its expression profile and function in barley, especially under abiotic stress. In this study, 22 GPAT genes were identified in the barley genome and divided into three groups (I, II, III), with the latter Group III subdivided further into three subgroups based on the phylogenetic analysis. The analyses of conserved motifs, gene structures, and the three-dimensional structure of HvGPAT proteins also support this classification. Through evolutionary analysis, we determined that HvGPATs in Group I were the earliest to diverge during 268.65 MYA, and the differentiation of other HvGPATs emerged during 86.83-169.84 MYA. The tissue expression profile showed that 22 HvGPAT genes were almost not expressed in INF1 (inflorescence 1). Many functional elements related to stress responses and hormones in cis-element analysis, as well as qRT-PCR results, confirm that these HvGPAT genes were involved in abiotic stress responses. The expression level of HvGPAT18 was significantly increased under abiotic stress and its subcellular localization indicated its function in the endoplasmic reticulum. Various physiological traits under abiotic stress were evaluated using transgenic Arabidopsis to gain further insight into the role of HvGPAT18, and it was found that transgenic seedlings have stronger resistance under abiotic stress than to the wild-type (WT) plants. Overall, our results provide new insights into the evolution and function of the barley GPAT gene family and enable us to explore the molecular mechanism of functional diversity behind the evolutionary history of these genes.

Function identification of Arabidopsis GPAT4 and GPAT8 in the biosynthesis of suberin and cuticular wax

Surface lipids in plants include cutin, cuticular wax and suberin. sn-Glycerol-3-phosphate acyltransferases (GPATs) facilitate the acylation of sn-glycerol-3-phosphate (G3P) utilizing a fatty acyl group from acyl-coenzyme A (acyl-CoA) or acyl-acyl carrier protein (acyl-ACP) as substrates for the biosynthesis of plant extracellular lipids such as suberin and cutin. Here we found that Arabidopsis GPAT4 and GPAT8 are specifically expressed in endodermis cells of roots where suberin was accumulated. GPAT4 mutation significantly decreased the amounts of the C16 and C18 ω-oxidized suberin monomers, whereas the mutation of GPAT8 had little effect on the suberin production, and the functions of both were not redundant. Root suberin phenotype analysis of gpat4-1 and gpat6-1 single or double mutant revealed that GPAT4 and GPAT6 play redundant functions. Interestingly, the gpat4-1 gpat8-1 double mutant displayed a glossy stem phenotype since fewer wax crystals were accumulated. This phenotype was not shown in either parent. Further study showed that the amounts of most wax components were significantly decreased. Taken together, our findings revealed that GPAT4 has an additive effect with GPAT6 in the root suberin biosynthesis, and plays a redundant role in wax production with GPAT8.

Genome-wide-association study and transcriptome analysis reveal the genetic basis controlling the formation of leaf wax in Brassica napus

Cuticular wax protects plants from various biotic and abiotic stresses. However, the genetic network of wax biosynthesis and the environmental factors influencing leaf wax production in rapeseed (Brassica napus) remains unclear. Here, we demonstrated the role of leaf wax in the resistance to Sclerotinia infection in rapeseed. We found that leaves grown under high light intensity had higher expression of genes involved in wax biosynthesis, and produced more wax on the leaf surface, compared with those grown under low light conditions. Genome-wide association study (GWAS) identified 89 single nucleotide polymorphisms significantly associated with leaf wax coverage. A cross-analysis between GWAS and differentially expressed genes (DEGs) in the leaf epidermis of the accessions with contrasting differences in wax content revealed 17 candidate genes that control this variation in rapeseed. Selective sweep analysis combined with DEG analysis unveiled 510 candidate genes with significant selective signatures. From the candidate genes, we selected BnaA02.LOX4, a putative lipoxygenase, and BnaCnn.CER1, BnaA02.CER3, BnaC02.CER3, and BnaA01.CER4 (ECERIFERUM1-4) that were putatively responsible for wax biosynthesis, to analyse the allelic forms and haplotypes corresponding to high or low leaf wax coverage. These data enrich our knowledge about wax formation, and provide a gene pool for breeding an ideal leaf wax content in rapeseed.

The core triacylglycerol toolbox in woody oil plants reveals targets for oil production bioengineering

Woody oil plants are the most productive oil-bearing species that produce seeds with high levels of valuable triacylglycerols (TAGs). TAGs and their derivatives are the raw materials for many macromolecular bio-based products, such as nylon precursors, and biomass-based diesel. Here, we identified 280 genes encoding seven distinct classes of enzymes (i.e., G3PAT, LPAAT, PAP, DGAT, PDCT, PDAT, and CPT) involved in TAGs-biosynthesis. Several multigene families are expanded by large-scale duplication events, such as G3PATs, and PAPs. RNA-seq was used to survey the expression profiles of these TAG pathway-related genes in different tissues or development, indicating functional redundancy for some duplicated genes originated from the large-scale duplication events, and neo-functionalization or sub-functionalization for some of them. Sixty-two genes showed strong, preferential expression during the period of rapid seed lipid synthesis, suggesting that their might represented the core TAG-toolbox. We also revealed for the first time that there is no PDCT pathway in Vernicia fordii and Xanthoceras sorbifolium. The identification of key genes involved in lipid biosynthesis will be the foundation to plan strategies to develop woody oil plant varieties with enhanced processing properties and high oil content.

Longer Duration of Active Oil Biosynthesis during Seed Development Is Crucial for High Oil Yield-Lessons from Genome-Wide In Silico Mining and RNA-Seq Validation in Sesame

Sesame, one of the ancient oil crops, is an important oilseed due to its nutritionally rich seeds with high protein content. Genomic scale information for sesame has become available in the public databases in recent years. The genes and their families involved in oil biosynthesis in sesame are less studied than in other oilseed crops. Therefore, we retrieved a total of 69 genes and their translated amino acid sequences, associated with gene families linked to the oil biosynthetic pathway. Genome-wide in silico mining helped identify key regulatory genes for oil biosynthesis, though the findings require functional validation. Comparing sequences of the SiSAD (stearoyl-acyl carrier protein (ACP)-desaturase) coding genes with known SADs helped identify two SiSAD family members that may be palmitoyl-ACP-specific. Based on homology with lysophosphatidic acid acyltransferase (LPAAT) sequences, an uncharacterized gene has been identified as SiLPAAT1. Identified key regulatory genes associated with high oil content were also validated using publicly available transcriptome datasets of genotypes contrasting for oil content at different developmental stages. Our study provides evidence that a longer duration of active oil biosynthesis is crucial for high oil accumulation during seed development. This underscores the importance of early onset of oil biosynthesis in developing seeds. Up-regulating, identified key regulatory genes of oil biosynthesis during early onset of seed development, should help increase oil yields.