Exocyst subunits EXO70B1 and B2 contribute to stomata dynamics and cell wall modifications

Matěj Drs¹Karel Muller¹Aline Voxeur²Natalia Lorena Serrano Saavedra¹Samantha Vernhettes²Eliška Škrabálková¹Jitka Ortmannová¹Martin Potocký¹Viktor Zarsky¹Tamara Pecenkova^1*

• ¹Institute of Experimental Botany, Academy of Sciences of the Czech Republic, Prague, Czechia
• ²Institut Jean-Pierre Bourgin, Versailles, France

Based on previous reports of defense-related defects in Arabidopsis loss-of-function (LOF) mutants of the EXO70B1 and EXO70B2 exocyst subunits, we investigated the underlying causes of these phenotypes. We analyzed stomatal aperture states in both young and adult plants and discovered a more closed initial state of stomatal opening in exo70Bs mutants. As the exocyst is involved in the secretion to the cell wall, we examined cell wall composition, and we correlated these findings with a comprehensive mRNA expression analysis. Our results revealed altered methylation and acetylation modifications of pectin and hemicellulose in the studied mutant lines. These changes in cell wall modifications may contribute to both compromised stomatal aperture-dependent and -independent defense responses, as well as to the transcriptional activation of defense pathways observed in non-infected mature mutant plants at adult developmental stages. Several candidate genes involved in these processes were pinpointed by RNAseq analysis. Interestingly, although the primary phenotypic and RNAseq deviations in young mutant lines may be specific for each of the two EXO70B mutant lines, they exhibit converging gene expression profiles in later developmental stages. This convergence may reflect the shared evolutionary origin of the two Brassicaceae EXO70 isoforms by a duplication from a common ancestral gene.