Abstract
Vacuolar invertase (VI) can irreversibly degrade sucrose into glucose and fructose and involve in plants abiotic-stress-tolerance. Cucumber (Cucumis sativus L.) is susceptible to drought stress, especially during the seedling stage. To date, the involvement of VI in drought tolerance in cucumber seedlings is in urgent need of exploration. In the present study, a cucumber vacuolar invertase gene, CsVI2, was isolated and functionally characterized. The results showed that (1) CsVI2 showed vacuolar invertase activity both in vivo and in vitro; (2) the transcript level of CsVI2, along with VI activity, was significantly induced by drought stress. Moreover, the expression of sucrose synthase 3 (CsSUS3) was increased and that of sucrose phosphate synthase 1 (CsSPS1) was decreased after exposure to drought stress, which was followed by an increase in sucrose synthase activity and a decrease in sucrose phosphate synthase activity; (3) CsVI2-overexpressing transformed cucumber seedlings showed enhanced vacuolar invertase activity and drought tolerance and 4) protein–protein interaction modelling indicated that a cucumber invertase inhibitor, CsINVINH3, can interact with CsVI2. In summary, the results indicate that CsVI2 as an invertase can regulate sucrose metabolism and enhance drought stress in cucumber seedlings.
Highlights
Sucrose metabolism plays important roles in plant development, yield formation and stress response [1]
Invertase is a key enzyme in sucrose hydrolysis that can hydrolyze sucrose into glucose and fructose [5], plays vital roles in providing carbon nutrients to plants and plays major roles in sugar signaling and tissue development [1,2]
The results showed that recombinant CsVI2 protein can hydrolyze sucrose into glucose and fructose after coincubation with sucrose with almost no affinity to other sugars—inulin and levan (Figure 3a)
Summary
Sucrose metabolism plays important roles in plant development, yield formation and stress response [1]. Sucrose is the end product of photosynthesis and is the major form of carbon that is transported from the source, mainly from leaves to sinks, such as fruit and roots [2]. Sucrose is further enzymatically degraded into glucose and fructose to provide energy and carbon sources for various metabolic processes [1,2]. Sucrose hydrolysis was conducted by sucrose synthase (SUS) and invertase. Invertase is a key enzyme in sucrose hydrolysis that can hydrolyze sucrose into glucose and fructose [5], plays vital roles in providing carbon nutrients to plants and plays major roles in sugar signaling and tissue development [1,2]
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