Stomatal CO₂-responses at sub- and above-ambient CO₂levels employ different pathways in Arabidopsis

Abstract

Stomatal pores, formed of paired guard cells, mediate CO2 uptake for photosynthesis and water loss via transpiration in plants. Globally rising atmospheric CO2 concentration triggers stomatal closure, contributing to increased leaf temperature and reduced nutrient uptake due to lower transpiration rate. Hence, it is important to understand the signalling pathways that control elevated CO2-induced stomatal closure to identify targets for breeding climate-ready crops. CO2-induced stomatal closure can be studied by increasing CO2 concentration from ambient to above-ambient concentrations, or elevation of CO2 levels from sub-ambient to above-ambient. Previous experiments comparing ferns with angiosperms suggested that stomatal responses to CO2 may be different, when changing CO2 levels in the sub-ambient or above-ambient ranges. Here, we set out to test this by comparing CO2-induced stomatal closure in key guard cell signalling mutants in response to CO2 elevation from 100 to 400 ppm or 400 to 800 ppm. We show that signalling components that contribute to CO2-induced stomatal closure are different in the sub-ambient and above-ambient CO2 levels, with guard cell slow-type anion channel SLAC1 involved mainly in above-ambient CO2-induced stomatal closure.

Countering elevated CO2 induced Fe and Zn reduction in Arabidopsis seeds

“…However, they retain wild-type stomatal responses to ABA, light and darkness. Together, with the work on beta CA1 and 4 (Hu et al, 2010(Hu et al, , 2021Hõrak et al, 2021) these results emphasise the importance of carbonic anhydrase enzyme activity in guard cell CO2 signalling and also show that manipulation of the ACA7 gene can help mitigate the effects of elevated CO2 on seed accumulation of Fe and Zn in Arabidopsis.…”

“…In response to a transition of 400 to 800 ppm CO 2 the double mutant closed its stomata slower than wild-type and overall, while significant the impact of lacking the βCAs was smaller at high CO 2 (Hõrak et al, 2021). It is interesting that we observed impaired responses to 1000 ppm CO 2 in aca7, whereas lesions in CO 2 -induced stomatal closure were only observed in βca1βca4 (Hu et al, 2010(Hu et al, , 2015Hõrak et al, 2021) New Phytologist might imagine that βCAs could compensate for the loss of an αCA. The lack of compensation might reflect ACA7 and βCA1, βCA4 being expressed in different cellular compartments or that ACA7 has other unknown functions or protein partners that cannot be complemented by βCA1, βCA4.…”

“…Recent work on the Arabidopsis βca1βca4 concluded that beta carbonic anhydrases (βCAs) have a significant role in mediating the stomatal closure response induced by transitions from 100 to 400 ppm CO 2 . In response to a transition of 400 to 800 ppm CO 2 the double mutant closed its stomata slower than wild‐type and overall, while significant the impact of lacking the βCAs was smaller at high CO 2 (Hõrak et al ., 2021). It is interesting that we observed impaired responses to 1000 ppm CO 2 in aca7 , whereas lesions in CO 2 ‐induced stomatal closure were only observed in βca1βca4 (Hu et al ., 2010, 2015; Hõrak et al ., 2021).…”

“…In response to a transition of 400 to 800 ppm CO 2 the double mutant closed its stomata slower than wild‐type and overall, while significant the impact of lacking the βCAs was smaller at high CO 2 (Hõrak et al ., 2021). It is interesting that we observed impaired responses to 1000 ppm CO 2 in aca7 , whereas lesions in CO 2 ‐induced stomatal closure were only observed in βca1βca4 (Hu et al ., 2010, 2015; Hõrak et al ., 2021). One might imagine that βCAs could compensate for the loss of an αCA.…”

“…Each group is evolutionary distinct and their protein structures very different to each other (Hewett-Emmett & Tashian, 1996;Fabre et al, 2007;DiMario et al, 2017DiMario et al, , 2018. Previous work in Arabidopsis has revealed that the βCAs are involved in the control of stomatal conductance and development by CO 2 , with these processes being partially impaired in the βca1βca4 double mutant (Hu et al, 2010(Hu et al, , 2015Hõrak et al, 2021). βCAs have also been implicated in the control of stomatal responses to CO 2 in maize and rice (Chen et al, 2017;Kolbe et al, 2019).…”