Drought-dependent regulation of cell coupling in Arabidopsis leaf epidermis requires plasmodesmata protein NHL12.

The cytoplasms of most plant cells are connected by membrane-lined cell wall channels, the plasmodesmata (PD). Dynamic regulation of sugar, hormone and protein diffusion through PD is essential for plant development and stress responses. Understanding this regulation requires knowledge of factors and mechanisms that control PD permeability through the modulation of callose levels in the cell wall around PD openings. We investigated PD regulation in leaf epidermis cells in relation to drought stress in Arabidopsis thaliana. Upon finding PD-mediated cell wall permeability decreased by drought stress and the hormone ABA, we tested several PD-associated genes with drought-responsive expression for their involvement in this response. Mutants of NHL12 showed relatively low PD permeability that was unaffected by drought or ABA treatment. Overexpression of NHL12 in Nicotiana benthamiana epidermis cells increased PD permeability. Moreover, we show that NHL12 can potentially interact with the callose synthase-regulator NHL3 and we explored the effect of NHL12 abundance and/or lower interface permeability on ABA signaling genes. Our results indicate that NHL12 is a drought-responsive negative regulator of PD callose levels and, thereby, interface permeability. Results are discussed with regard to PD function during drought stress and the regulation of intercellular transport.