Functional Characterization of a Cucumber (Cucumis sativus L.) Vacuolar Invertase, CsVI1, Involved in Hexose Accumulation and Response to Low Temperature Stress

Abstract

Cucumber (Cucumis sativus L.), an important vegetable plant species, is susceptible to low temperature stress especially during the seedling stage. Vacuolar invertase (VI) plays important roles in plant responses to abiotic stress. However, the molecular and biochemical mechanisms of VI function in cucumber, have not yet been completely understood and VI responses to low temperature stress and it functions in cold tolerance in cucumber seedlings are also in need of exploration. The present study found that hexose accumulation in the roots of cucumber seedlings under low temperature stress is closely related to the observed enhancement of invertase activity. Our genome-wide search for the vacuolar invertase (VI) genes in cucumber identified the candidate VI-encoding gene CsVI1. Expression profiling of CsVI1 showed that it was mainly expressed in the young roots of cucumber seedlings. In addition, transcriptional analysis indicated that CsVI1 expression could respond to low temperature stress. Recombinant CsVI1 proteins purified from Pichia pastoris and Nicotiana benthamiana leaves could hydrolyze sucrose into hexoses. Further, overexpression of CsVI1 in cucumber plants could increase their hexose contents and improve their low temperature tolerance. Lastly, a putative cucumber invertase inhibitor was found could form a complex with CsVI1. In summary, these results confirmed that CsVI1 functions as an acid invertase involved in hexose accumulation and responds to low temperature stress in cucumber seedlings.

A Vacuolar Invertase CsVI2 Regulates Sucrose Metabolism and Increases Drought Tolerance in Cucumis sativus L.

“…The expression of CsVI2 was detectable in the leaves, roots and stems, and especially peaked in young leaves and young roots, according to our previous research [ 21 ]. To further understand the expressional parts of CsVI2 in young roots, young cucumber roots were divided into maturation regions, elongation regions and meristematic regions.…”

“…Previously, three cucumber putative vacuolar invertase genes have been screened, and only vacuolar invertase CsVI1 was functionally characterized by us [ 21 ]. In this study, CsVI2 (Csa5G1704590.1), was chosen for further research.…”

“…Expression of CsVI2 and VI activity were increased after exposure to drought stress in cucumber seedlings ( Figure 6 ). Besides CsVI2 , drought stress did not induce the CsVI1 expression in the transcript, and CsVI3 has been found almost no expression of in young cucumber seedling tissues [ 21 ]. The similar phenomenon was also found in maize [ 5 ], rice [ 26 ] and Arabidopsis [ 11 ].…”

“…After incubation, the reaction was stopped by heating at 95 °C for 5 min. The contents of fructose and glucose were measured by a coupled spectrophotometric enzyme assay, as described previously [ 21 ]. All enzyme measurements were performed under conditions where activities were linearly proportional to the amount of enzyme and incubation time.…”

Plant sugar metabolism, transport and signalling in challenging environments

“…In recent decades, there have been many attempts to improve response to environmental constraints by producing transgenic plants with modified sugar metabolism, transport or signalling (Pérez‐Díaz et al, 2021; Rodriguez et al, 2019; Sarkar & Sadhukhan, 2022). Significantly, the manipulation of sugar exchanges between cytosol and vacuole by targeting sugar metabolism or sugar transport has been proven to be essential for plant development and response to abiotic stresses (Chen et al, 2022; Feng et al, 2021; Qian et al, 2018; Saddhe et al, 2021; Valifard et al, 2021; Vu et al, 2020; Zhou et al, 2022). Despite the identification of numerous tonoplast sugar transporters, a functional characterisation for most of them is still missing.…”