Abstract
14-3-3s are highly conserved, multigene family proteins that have been implicated in modulating various biological processes. The presence of inherent polyploidy and genome complexity has limited the identification and characterization of 14-3-3 proteins from globally important Brassica crops. Through data mining of Brassica rapa, the model Brassica genome, we identified 21 members encoding 14-3-3 proteins namely, BraA.GRF14.a to BraA.GRF14.u. Phylogenetic analysis indicated that B. rapa contains both ε (epsilon) and non-ε 14-3-3 isoforms, having distinct intron-exon structural organization patterns. The non-ε isoforms showed lower divergence rate (Ks < 0.45) compared to ε protein isoforms (Ks > 0.48), suggesting class-specific divergence pattern. Synteny analysis revealed that mesohexaploid B. rapa genome has retained 1–5 orthologs of each Arabidopsis 14-3-3 gene, interspersed across its three fragmented sub-genomes. qRT-PCR analysis showed that 14 of the 21 BraA.GRF14 were expressed, wherein a higher abundance of non-ε transcripts was observed compared to the ε genes, indicating class-specific transcriptional bias. The BraA.GRF14 genes showed distinct expression pattern during plant developmental stages and in response to abiotic stress, phytohormone treatments, and nutrient deprivation conditions. Together, the distinct expression pattern and differential regulation of BraA.GRF14 genes indicated the occurrence of functional divergence of B. rapa 14-3-3 proteins during plant development and stress responses.
Highlights
14-3-3 proteins derived their unique name from the studies of fractionation of bovine brain proteins on DEAE cellulose and their electrophoretic mobility on starch gel electrophoresis (Moore and Perez, 1967)
The 14-3-3 proteins are a family of highly conserved regulatory proteins present across phyla, which function by binding to the phosphorylated target proteins to play vital roles in many biological processes in plants, including primary metabolism and hormone signaling as well as in response to the abiotic and biotic stresses
It is quite expected that the inherent polyploidy in plants has shaped the expansion of 14-3-3 gene family
Summary
14-3-3 proteins derived their unique name from the studies of fractionation of bovine brain proteins on DEAE cellulose and their electrophoretic mobility on starch gel electrophoresis (Moore and Perez, 1967). Current literatures clearly suggest the involvement of 14-3-3 proteins in various physiological processes including primary carbon and nitrogen metabolism (Comparot et al, 2003), abiotic and biotic stress responses (Roberts et al, 2002; Umezawa et al, 2004; Yan et al, 2004; Chen et al, 2006; Yang et al, 2013; Catalá et al, 2014; Zhou et al, 2014; He et al, 2015; Li et al, 2015), signaling pathways of phytohormones like ABA, GA, and BR (Testerink et al, 1999; Igarashi et al, 2001; Ryu et al, 2007; Kim et al, 2009; Zhou et al, 2015), and during plant growth and development (Radwan et al, 2012; de Boer et al, 2013; Sun et al, 2014; van Kleeff et al, 2014) To carry such diverse roles, almost all eukaryotes harbor multiple isoforms of 14-3-3 genes, with two present in yeast, seven in humans, and more than a dozen in vascular plants. The study provides an excellent base for conducting further in-depth research on various signaling pathways regulated by B. rapa 14-3-3 proteins, which could be utilized for agricultural improvements of the mustard crop
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