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.