Deciphering grass-specific mechanisms of cell polarization and asymmetric division during stomatal development

Objective

Stomata are specialized epidermal structures enabling gas-exchanges, key innovation for terrestrial plants but also weak spots regarding abiotic and biotic stresses. In most dicotyledons, stomata consist of two kidney-shaped guard cells, whereas grasses form a unique four-cell complex with two subsidiary cells (SCs) allowing faster stomatal opening and closing, contributing to water-use efficiency and stress resilience. As grasses include major cultivated plants in Europe, understanding how these specialized structures are formed and regulated is of central importance. The wild-grass model Brachypodium distachyon has been instrumental in addressing these questions. Studies revealed that, unlike in Arabidopsis thaliana, grass four-cell stomata require two successive asymmetric cell divisions (ACDs): first a transverse giving rise to the guard mother cell and then a longitudinal generating the SCs. POLAR and PL1 proteins, have emerged as central regulators of stomatal forming ACDs by establishing the future division plane through their pre-division polarity. While both act redundantly in stomatal precursor divisions in A. thaliana, results from my host lab point to a subfunctionalization in B. Distachyon. PL1 controls the first transverse ACD, whereas POLAR regulates the second longitudinal ACD. Despite differences in function and polarity, the POLAR family shares common polarity turn-over after division and overall role in ACD probably relying on post-translational regulation and specific partner interactions. Building on my expertise in protein biochemistry and the host lab’s knowledge of grass biology, the POLAR2M project aims to elucidate how POLAR and PL1 coordinate cell polarity and each ACD during stomatal and leaf epidermis development in grasses. Beyond fundamental insights, POLAR2M will shed light on molecular processes directly relevant to sustainable agricultural production, a major challenge for global food security.