Crosstalk between β-carbonic anhydrases and PsbS in the regulation of photosynthesis and stress tolerance in Arabidopsis.

Plant growth and stress responses are tightly linked to chloroplast retrograde signaling. Key regulators, such as the 22 kDa PSII protein (PsbS) and β-carbonic anhydrases (βCAs), have been implicated in photoprotection and stress acclimation. In this study, we investigated the effects of simultaneously overexpressing βCA1 and/or βCA2 in a PsbS-overexpressing Arabidopsis thaliana background. Double and triple transgenic lines (oePsbSoeβCA1 and oePsbSoeβCA1βCA2) showed enhanced photoprotection, improved acclimation to fluctuating light, and greater water use efficiency, but at the cost of reduced biomass relative to Col-0 and the npq4-1 mutant. Following bicarbonate fertilization, the triple overexpression line had improved biomass compared with oePsbS and npq4-1, but not compared with Col-0. Importantly, our data reveal that βCAs modulate PsbS abundance, supporting the existence of their crosstalk. Bicarbonate treatment activated stress-responsive genes and transcription factors exclusively in oePsbSoeβCA lines, indicating heightened sensitivity associated with elevated activity of βCAs. Together, these findings suggest a previously unrecognized regulatory link between the activity of βCAs and PsbS turnover in fine-tuning stress responses and productivity, mediated at least in part by changes in PsbS expression. However, the underlying molecular mechanisms require further investigation to determine whether these effects are specific to the PsbS level or reflect a broader role for βCAs.