Characterization of raffinose metabolism genes uncovers a wild Arachis galactinol synthase conferring tolerance to abiotic stresses

Christina C Vinson,Brenda N Porto,Iracyara Sampaio,Thomas C R Williams,Etienne G J Danchin,Patricia M Guimaraes,Ana P Z Mota,Ana L Lacerda,Thais N Oliveira,Ana C M Brasileiro

doi:10.1038/s41598-020-72191-4

Abstract

Raffinose family oligosaccharides (RFOs) are implicated in plant regulatory mechanisms of abiotic stresses tolerance and, despite their antinutritional proprieties in grain legumes, little information is available about the enzymes involved in RFO metabolism in Fabaceae species. In the present study, the systematic survey of legume proteins belonging to five key enzymes involved in the metabolism of RFOs (galactinol synthase, raffinose synthase, stachyose synthase, alpha-galactosidase, and beta-fructofuranosidase) identified 28 coding-genes in Arachis duranensis and 31 in A. ipaënsis. Their phylogenetic relationships, gene structures, protein domains, and chromosome distribution patterns were also determined. Based on the expression profiling of these genes under water deficit treatments, a galactinol synthase candidate gene (AdGolS3) was identified in A. duranensis. Transgenic Arabidopsis plants overexpressing AdGolS3 exhibited increased levels of raffinose and reduced stress symptoms under drought, osmotic, and salt stresses. Metabolite and expression profiling suggested that AdGolS3 overexpression was associated with fewer metabolic perturbations under drought stress, together with better protection against oxidative damage. Overall, this study enabled the identification of a promising GolS candidate gene for metabolic engineering of sugars to improve abiotic stress tolerance in crops, whilst also contributing to the understanding of RFO metabolism in legume species.

Highlights

Raffinose family oligosaccharides (RFOs) are implicated in plant regulatory mechanisms of abiotic stresses tolerance and, despite their antinutritional proprieties in grain legumes, little information is available about the enzymes involved in RFO metabolism in Fabaceae species
Whilst RFOs are major soluble sugars that are second only to sucrose in abundance in mature legume s eeds[13], very little is known about the genes involved in raffinose metabolism in Fabaceae species, with few examples described in Cicer arietinum and Glycine max[14,15]
The two belonging to the Fabaceae family (GLYMA Q7XZ08 and MEDSA Q84MZ5) were used as references for HMM profile construction. Using this HMM profile, 30 proteins from 11 Fabaceae species were identified in UniProt as putatively belonging to the galactinol synthase (GolS) family (Table S2), together with five proteins each for A. duranensis and A. ipaënsis genomes

Summary

Introduction

Raffinose family oligosaccharides (RFOs) are implicated in plant regulatory mechanisms of abiotic stresses tolerance and, despite their antinutritional proprieties in grain legumes, little information is available about the enzymes involved in RFO metabolism in Fabaceae species. The systematic survey of legume proteins belonging to five key enzymes involved in the metabolism of RFOs (galactinol synthase, raffinose synthase, stachyose synthase, alpha-galactosidase, and beta-fructofuranosidase) identified 28 coding-genes in Arachis duranensis and 31 in A. Complex molecular networks are activated to allow plants to cope with stressful conditions[2], including modifications in plant metabolism to produce a series of low molecular weight compounds that accumulate in the cytosol or vacuole, such as soluble sugars, amines and amino acids[3] These compounds participate in osmotic adjustment, stabilize cell components, provide membrane protection, and scavenge excess Reactive Oxygen Species (ROS)[4]. In peanut (Arachis hypogaea), the second most cultivated grain legume in the world after soybean, seeds accumulate high amounts of indigestible RFOs, which limits its consumption[13,17]

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