Metabolic process of raffinose family oligosaccharides during cold stress and recovery in cucumber leaves

Abstract

Raffinose family oligosaccharides (RFOs) accumulate under stress conditions in many plants and have been suggested to act as stress protectants. To elucidate the metabolic process of RFOs under cold stress, levels of RFOs, and related carbohydrates, the expression and activities of main metabolic enzymes and their subcellular compartments were investigated during low-temperature treatment and during the recovery period in cucumber leaves. Cold stress induced the accumulation of stachyose in vacuoles, galactinol in vacuoles and cytosol, and sucrose and raffinose in vacuoles, cytosol, and chloroplasts. After cold stress removal, levels of these sugars decreased gradually in the respective compartments. Among four galactinol synthase genes (CsGS), CsGS1 was not affected by cold stress, while the other three CsGSs were up-regulated by low temperature. RNA levels of acid-α-galactosidase (GAL) 3 and alkaline-α-galactosidase (AGA) 2 and 3, and the activities of GAL and AGA, were up-regulated after cold stress removal. GAL3 protein and GAL activity were exclusively located in vacuoles, whereas AGA2 and AGA 3 proteins were found in cytosol and chloroplasts, respectively. The results indicate that RFOs, which accumulated during cold stress in different subcellular compartments in cucumber leaves, could be catabolized in situ by different galactosidases after stress removal.

Responses of Manila Grass (Zoysia matrella) to chilling stress: From transcriptomics to physiology

“…Accordingly, three GO terms including “response to sucrose” (GO:0009744), “response to glucose” (GO:0009749) and “response to fructose” (GO:0009750) were enriched among the DEGs, suggesting the accumulation of these sugars. Raffinose family oligosaccharides (RFOs) are α-1, 6-galactosyl extensions of sucrose [ 77 ] and have been reported to accumulate significantly under low temperature stress [ 78 – 80 ]. Stachyose synthase, galactinol synthase and galactinol-sucrose galactosyltransferase are important for the biosynthesis of RFOs.…”

Characteristics and expression patterns of six α-galactosidases in cucumber (Cucumis sativus L.)

“…galactan galactosyltransferase and acid galactosidase [10], indicating the vacuolar subcellular localization of this group of α-Gals; Both CsAGA3 and AAL90901 belong to the AGA3 group and were found to distribute in chloroplasts [6,9], etc. However, it is also common that some α-Gals classified into different groups revealed similar functions, while other α-Gals with different biological roles belong to the same group (Fig 3).…”

“…Normally, there are multiple copies of both acid α-Gals and alkaline α-Gals in plant genomes. According to their subcellular localization, acid α-Gals were further divided into two groups, apoplastic α-Gals and vacuolar α-Gals [9,10]. The signal peptide of apoplastic α-Gals involve in secretory pathway, which may target them into the extracellular space to hydrolyze cell wall-associated galactomannan during seed maturation or germination [11].…”

“…Comparing with apoplastic α-Gals, the research about vacuolar α-Gals is rare. It is reported a cucumber vacuolar α-Gal is responsible for consuming raffinose family oligosaccharides (RFOs) in vacuole after stress removal [9]. Alkaline α-Gals, with an optimal pH of 7-8, was initially reported in Cucurbita pepo leaves [14].…”

“…In addition, RFOs are synthesized in mature cucumber seeds, which were rapidly decomposed by α-Gals after imbibition [25]. RFOs also accumulate in different cucumber organs under cold stress and then are consumed by α-Gals after stress removal [9,26]. In the cucumber genome, there are six putative α-Gal genes, three acid α-Gal genes (CsGAL1, CsGAL2, and CsGAL3) and three alkaline α-Gal genes (CsAGA1, CsAGA2, and CsAGA3).…”