Identification of Loci Involved in ρ[CO2] Regulation of Epidermal Patterning and Stomatal Development

The epidermis of mature Arabidopsis thaliana leaves is a jigsaw puzzle of pavement cells, perforated non-randomly with stomatal pores defined by pairs of guard cells. The pattern is sensitive to environmental factors, including ρ[CO₂]- an important driver of climate change and a primary limitation to productivity of C3 plants.  In general, Arabidopsis leaves decrease their number of stomata in response to elevated ρ[CO₂] by 20%, but there is considerable variation within a population.  The mechanism regulating this response is unknown, but common hypotheses for ρ[CO₂] regulation of stomatal patterning suggest the pathway is either regulated downstream of photosynthetic outputs, by extracuticular wax quantity, or through extracellular protein signaling.  To test these hypotheses, quantitative trait mapping of a recombinant inbred population (n = 165) derived from parental lines with contrasting epidermal responses to ρ[CO₂] has been performed to identify the underlying genetic mechanisms that mediate environmental control of epidermal cell type distribution in the leaf epidermis.   Plants were grown under 1500ppm ρ[CO₂] and large scale, accurate and quantitative measurements of epidermal cell parameters, including stomatal size, stomatal index, pavement cell size, lobe number, and surface area were collected.  These data sets were collected using optical topometry, a novel, high-throughput, and non-destructive platform for measuring epidermal surface topography.  Preliminary results suggest that heritability of ρ[CO₂] regulation over epidermal development may be lower than previous studies originally suggested.