Raffinose family oligosaccharides (RFOs): role in seed vigor and longevity

Abstract

Seed vigor and longevity are important agronomic attributes, as they are essentially associated with crop yield and thus the global economy. Seed longevity is a measure of seed viability and the most essential property in gene bank management since it affects regeneration of seed recycling. Reduced seed life or storability is a serious issue in seed storage since germplasm conservation and agricultural enhancement initiatives rely on it. The irreversible and ongoing process of seed deterioration comprises a complex gene regulatory network and altered metabolism that results in membrane damage, DNA integrity loss, mitochondrial dysregulation, protein damage, and disrupted antioxidative machinery. Carbohydrates and/or sugars, primarily raffinose family oligosaccharides (RFOs), have emerged as feasible components for boosting or increasing seed vigor and longevity in recent years. RFOs are known to perform diverse functions in plants, including abiotic and biotic stress tolerance, besides being involved in regulating seed germination, desiccation tolerance, vigor, and longevity. We emphasized and analyzed the potential impact of RFOs on seed vigor and longevity in this review. Here, we comprehensively reviewed the molecular mechanisms involved in seed longevity, RFO metabolism, and how RFO content is critical and linked with seed vigor and longevity. Further molecular basis, biotechnological approaches, and CRISPR/Cas applications have been discussed briefly for the improvement of seed attributes and ultimately crop production. Likewise, we suggest advancements, challenges, and future possibilities in this area.

Keywords: Galactinol; RFO; plant biology; seed.

Figure 1. Schematic pathway of RFO family metabolism in plants

(A) RFOs biosynthesis pathway: RFO biosynthesis is initiated by the conversion of Myo-inositol and UDP-Galactose into galactinol utilizing GolS. The galactinol further acts as galactosyl moiety donor for generation of successive RFO members like raffinose, stachyose, verbascose, and ajugose utilizing indicated enzymes in the pathway. This pathway is called galactinol-dependent. in galactinol independent pathway, GGT catalyses the direct transfer of the galactosyl moiety from one RFO molecule to another and leads to the formation of RFO members; GGT, galactan-galactosyltransferase; GolS, galactinol synthase; RAFS, raffinose synthase; STS, stachyose synthase; VES, verbascose synthase. (B) RFOs catabolic pathway: RFOs are digested or catabolized first into galatose-1-phsophate via GALK that further has two fates. One is Lelior pathway where it produces glucose-1-phosphate via GALT and other one is to undergo alternative pathway where the end products are UDP-glucose and UDP-galactose catalysed by GALE; GALE, UDP-galactose 4′-epimerase; GALK, galactokinase; GALT, galactose-1-phosphate uridyltransferase.

Figure 2. Role and the underlying mechanisms of RFOs in regulating the seed vigor and longevity or overall seed health