Functional analysis of bCA1 splice forms in stomatal CO2 responses

Abstract

Plants tightly control their stomatal apertures to balance CO2 uptake for photosynthesis with water loss through transpiration. Elevated CO2 causes stomata to close, whereas low CO2 triggers stomatal opening. Carbonic anhydrases (CAs) have been implicated as key upstream regulators of guard cell CO2 signaling. Although four different splice forms of bCA1 with distinct subcellular localization have been identified to date, only the longest chloroplast-localized bCA1.2 has been shown to play a role in stomatal CO2 responses. Moreover, there is uncertainty in the literature regarding the localization of different bCA1 splice forms. This thesis aimed to verify the subcellular localization of bCA1 splice forms and determine their role in guard cell CO2 signaling. In addition, we have identified a putative kinase-interaction motif (KIM) in bCA1 and aimed to explore the effect of its disruption on the localization and function of bCA1.3. Our results indicate that splice forms bCA1.2 and bCA1.3 are localized to chloroplasts, whereas bCA1.1 and bCA1.4 are cytosolic proteins. Using transgenic Arabidopsis plants, we demonstrate that all four splice forms can function in guard cell CO2 signaling. Destroying the putative KIM affected both the localization and function of bCA1.3, although the mechanisms behind these effects remain to be elucidated.