Evolutionary diversification of galactinol synthases in Rosaceae: adaptive roles of galactinol and raffinose during apple bud dormancy.

Vítor da Silveira Falavigna,Giancarlo Pasquali,Diogo Denardi Porto,Luís Fernando Revers,Yohanna Evelyn Miotto,Henrique Pessoa dos Santos,Paulo Ricardo Dias de Oliveira,Márcia Margis-Pinheiro

doi:10.1093/jxb/erx451

Abstract

Galactinol synthase (GolS) is a key enzyme in the biosynthetic pathway of raffinose family oligosaccharides (RFOs), which play roles in carbon storage, signal transduction, and osmoprotection. The present work assessed the evolutionary history of GolS genes across the Rosaceae using several bioinformatic tools. Apple (Malus × domestica) GolS genes were transcriptionally characterized during bud dormancy, in parallel with galactinol and raffinose measurements. Additionally, MdGolS2, a candidate to regulate seasonal galactinol and RFO content during apple bud dormancy, was functionally characterized in Arabidopsis. Evolutionary analyses revealed that whole genome duplications have driven GolS gene evolution and diversification in Rosaceae speciation. The strong purifying selection identified in duplicated GolS genes suggests that differential gene expression might define gene function better than protein structure. Interestingly, MdGolS2 was differentially expressed during bud dormancy, concomitantly with the highest galactinol and raffinose levels. One of the intrinsic adaptive features of bud dormancy is limited availability of free water; therefore, we generated transgenic Arabidopsis plants expressing MdGolS2. They showed higher galactinol and raffinose contents and increased tolerance to water deficit. Our results suggest that MdGolS2 is the major GolS responsible for RFO accumulation during apple dormancy, and these carbohydrates help to protect dormant buds against limited water supply.

Highlights

Gene and genome duplication events have yielded the Whole-genome duplication (WGD) has been a common fearaw genetic material for biological evolution, with a major ture during angiosperm speciation and is considered to be a impact on most eukaryotes, including plants (Zhang, 2003). driving force in evolution due to the innovations associated1248 | Falavigna et al.with these events (Jiao et al, 2011)
MdGolS1, 2, 3, and 4 cDNA sequences showed differences in comparison with the genomic sequences: one nucleotide mismatch without amino acid change, a misprediction in the second exon that resulted in 27 additional nucleotides, three nucleotide mismatches leading to two amino acid changes, and 17 mismatches leading to four amino acid changes, respectively (Supplementary Fig. S2)
Galactinol synthase is a key enzyme in the biosynthetic pathway of raffinose family oligosaccharide (RFO), which are carbohydrates that play important roles in carbon storage, signal transduction, and osmoprotection, among others (Elsayed et al, 2014; Sengupta et al, 2015)

Summary

Introduction

Gene and genome duplication events have yielded the Whole-genome duplication (WGD) has been a common fearaw genetic material for biological evolution, with a major ture during angiosperm speciation and is considered to be a impact on most eukaryotes, including plants (Zhang, 2003). driving force in evolution due to the innovations associated1248 | Falavigna et al.with these events (Jiao et al, 2011). Apples underwent a recent WGD event around 50 MYA that is restricted to the Pyreae clade, which encompasses pear and various other Rosaceae genera (Velasco et al, 2010; Wu et al, 2013; Xiang et al, 2017). These events triggered the emergence of specific subclades of genes, resulting in unique developmental and metabolic traits

Methods

Results

Conclusion