5 years ago

SHORTROOT-mediated increase in stomatal density has no impact on photosynthetic efficiency.

Peter Westhoff, Mara L Schuler, Olga V Sedelnikova, Berkley J Walker, Jane A Langdale
The co-ordinated positioning of veins, mesophyll cells and stomata across a leaf is crucial for efficient gas exchange and transpiration, and therefore for overall function. In monocot leaves, stomatal cell files are positioned at the flanks of underlying longitudinal leaf veins, rather than directly above or below. This pattern suggests either that stomatal formation is inhibited in epidermal cells directly in contact with the vein, or that specification is induced in cells files beyond the vein. The SHORTROOT pathway specifies distinct cell-types around the vasculature in sub-epidermal layers of both root and shoots, with cell-type identity determined by distance from the vein. To test whether the pathway has the potential to similarly pattern epidermal cell-types, we expanded the expression domain of the rice OsSHR2 gene, which we show is restricted to developing leaf veins, to include bundle sheath cells encircling the vein. In transgenic lines, which were generated using the orthologous ZmSHR1 gene to avoid potential silencing of OsSHR2, stomatal cell files were observed both in the normal position and in more distant positions from the vein. Contrary to theoretical predictions, and to phenotypes observed in eudicot leaves, the increase in stomatal density did not enhance photosynthetic capacity or increase mesophyll cell density. Collectively these results suggest that the SHORTROOT pathway may co-ordinate the positioning of veins and stomata in monocot leaves, and that distinct mechanisms may operate in monocot and eudicot leaves to co-ordinate stomatal patterning with the development of underlying mesophyll cells.

Publisher URL: http://doi.org/10.1104/pp.17.01005

DOI: 10.1104/pp.17.01005

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