Three Homologous Genes Encodingsn-Glycerol-3-Phosphate Acyltransferase 4 Exhibit Different Expression Patterns and Functional Divergence inBrassica napus       

Abstract

T9C 1T4 (A.E.-M., S.S.)Brassica napus is an allotetraploid (AACC) formed from the fusion of two diploid progenitors, Brassica rapa (AA) and Brassica oleracea (CC). Polyploidy and genome-wide rearrangement during the evolution process have resulted in genes that are present as multiple homologs in the B. napus genome. In this study, three B. napus homologous genes encoding endoplasmic reticulumbound sn-glycerol-3-phosphate acyltransferase 4 (GPAT4) were identified and characterized. Although the three GPAT4 homologs share a high sequence similarity, they exhibit different expression patterns and altered epigenetic features. Heterologous expression in yeast further revealed that the three BnGPAT4 homologs encoded functional GPAT enzymes but with different levels of polypeptide accumulation. Complementation of the Arabidopsis (Arabidopsis thaliana) gpat4 gpat8 double mutant line with individual BnGPAT4 homologs suggested their physiological roles in cuticle formation. Analysis of gpat4 RNA interference lines of B. napus revealed that the BnGPAT4 deficiency resulted in reduced cutin content and altered stomatal structures in leaves. Our results revealed that the BnGPAT4 homologs have evolved into functionally divergent forms and play important roles in cutin synthesis and stomatal development.Polyploidy has long been considered a prominent evolutionary force for flowering plants ( Udall and Wendel, 2006). Over 95% of the lineages of angiosperms have undergone at least one event of polyploidization over their evolutionary time, suggesting that most of the existing flowering plants evolved from ancient polyploids (Bennett and Leitch, 1997;Chen, 2007;Gaeta et al., 2007). Polyploidy, along with genomic segmental duplications, could benefit plants by increasing overall gene expression levels and cell sizes and providing sources for novel variants and genome "buffering" of deleterious mutations (Udall and Wendel, 2006). Genes duplicated by such events could undergo three primary evolutionary fates over the long term (Wendel, 2000;Blanc and Wolfe, 2004;Lukens et al., 2004;Whittle and Krochko, 2009): (1) pseudogenization (loss or silencing), whereby duplicated genes with redundant functions accumulate deleterious mutations and are eventually lost without detrimental effects on plant fitness; (2) neofunctionalization, whereby some redundant genes develop new adaptive functions by positive Darwinian selection; and (3) subfunctionalization, a process in which the ancestral gene functions become subdivided among the duplicated genes.Brassica napus (AACC; n = 19) is an allotetraploid oilseed crop that evolved from the hybridization of two diploid progenitors, Brassica rapa (AA; n = 10) and Brassica oleracea (CC; n = 9) during human cultivation (over 10,000 years ago; U, 1935;Cheung et al., 2009). The Brassica species are closely related to the model plant Arabidopsis (Arabidopsis thaliana), all of which belong to the same tribe (Brassiceae) and share a common recent ancestry (20 million years ago; Yang et al., 1999). Comparative...

A Land-Plant-Specific Glycerol-3-Phosphate Acyltransferase Family in Arabidopsis: Substrate Specificity, sn-2 Preference, and Evolution

“…agreement with the results in Arabidopsis, increases or decreases of C16/C18 leaf cutin monomers are observed after ectopic expression of a GPAT4/8 homolog from Echium pitardii in tobacco (Mañas-Fernández et al, 2010) or by silencing of GPAT4 homologs in Brassica napus (Chen et al, 2011b). Thus, for most monomers, the in vivo data coincide with in vitro enzyme specificity data.…”

Isolation and expression analysis of glycerol-3-phosphate acyltransferase genes from peanuts (<em><em>Arachis hypogaea</em></em> L.)

“…Although the enzymatic activity of AtGPAT9 has not been directly confirmed and its physiological function is unknown, polypeptide sequence alignment, phylogenetic analysis, conserved domain analysis and gene expression data have all suggested that AtGPAT9 may play an essential role in the synthesis of membrane and storage lipids in plants (Gidda et al, 2009;Chen et al, 2011b). Expression profiling revealed that the levels and tissue-specific accumulations of AhGPAT9 transcript are distinct from those of other GPAT family members, which is consistent with the more diverged nature of the AtGPAT9 gene.…”

“…In Brassica napus, three homologous GPAT4 genes exhibited different expression patterns and distinct epigenetic features. A phenotypic rescue of a gpat4 gpat8 Arabidopsis double mutant and analysis of the gpat4 RNAi lines of B. napus suggested physiological roles of GPAT4s in cuticle formation of the rosette leaves, early flower development, pollen development, and the biosynthesis of storage lipids (Chen et al, 2011b). Two homologous GPAT genes isolated from Echium pitardii have high similarity to the AtGPAT4/8 genes of Arabidopsis.…”

MYB107 and MYB9 Homologs Regulate Suberin Deposition in Angiosperms

“…Expression analysis of GPAT family members in the SlDCR-RNAi fruit revealed that only Solyc04g011600 (SlGPAT5) displayed a significantly altered expression, showing a >350-fold increase in expression compared with wild-type fruit skin ( Figure 1G; Supplemental Figure 5B). Importantly, SlGPAT4 and SlGPAT6, considered to be involved in cutin polymer formation (Yang et al, 2010;Chen et al, 2011b;Petit et al, 2016), showed no change in expression (Supplemental Figure 5).…”