Esterified-pectin-coupled polar stiffening controls grass stomatal opening.

Stomata are pivotal for gas exchange during photosynthesis and transpiration and are therefore critical in plant growth and global water cycles. However, the mechanistic role of cell wall architecture in grass stomatal function remains elusive. Here immunolabelling and mechanical mapping revealed local distribution of methylesterified pectin at the stiffer polar ends of maize stomata. Expression-knockdown maize with reduced pectin labelling showed decreased polar stiffness and increased stomatal aperture. Finite element modelling corroborated these findings, suggesting that in contrast to non-grass stomata, the size and modulus of the polar materials limit maize stomatal opening. Surveys from various plant species suggest that polar-enriched methylesterified pectin is a unique feature of grass stomata. Xylanase pretreatment diminished pectin labelling at the polar ends, implying associations between pectin and xylan. Our multi-scale research uncovers a pectin-xylan-cellulose composite mediating polar fixation during maize stomatal movement, unveiling new targets for stomata engineering and crop breeding.