Speeding up or slowing down stomatal opening? The route(s) toward WUE improvement
It has been estimated that slower stomatal opening can limit A by up to 10% (McAusland et al., 2016). Thus, increasing stomatal speediness through plant metabolic engineer could leads to increased crop yield and/or WUE (Lawson & Vialet-Chabrand, 2019). Indeed, optogenetic manipulation of a synthetic light-gated K+channel (BLINK1 ) increased stomatal speediness to light and ultimately leads to increased biomass production without major impacts in water use by the plant (Papanatsiou et al., 2019). However, such engineered faster stomata could lead to unnecessary water losses in crops grown under extreme dry conditions. Thus, it is important to highlight that the strategies to improve crop WUE through genetic engineering should consider the water regime of the environment in which the plants will grow (Gago et al., 2014). In this context, our results highlight that slower stomatal responses and reducedg s and WPT could also represent advantages for plants growing under fluctuating and dry conditions. An alternative possibility is thus to obtain stomata with faster closure and slower opening, in a scenario which A is not highly restricted byg s during light imposition, i.e. the slower stomatal opening would not have substantial impacts on A , as observed in different angiosperms species (McAusland et al., 2016). Given that the mechanisms that regulate stomatal opening and closure differ substantially, it is possible to achieve this target through manipulation of the key regulators of both processes. However, several research has yet to be done to unveil the key regulators of stomatal speediness.
In conclusion, tobacco transgenic plants with antisense construction target to guard cell NtSUS2 had slower stomatal opening in the light and decreased steady-state g s and WPT under well-watered conditions. Furthermore, the transgenic lines showed higher or lower reduction in WPT under short water restriction periods, indicating a greater effective use of water under these conditions. Our results provide further evidence that NtSUS2 is an important regulator of guard cell metabolic network and strengthen the idea that engineering guard cell metabolism is a promising strategy to decrease crop water consumption toward WUE improvement.