A Genetic Dissection of Natural Variation for Stomatal Abundance Traits in .

Stomatal abundance varies widely across natural populations of , and presumably affects plant performance because it influences water and CO exchange with the atmosphere and thence photosynthesis and transpiration. In order to determine the genetic basis of this natural variation, we have analyzed a recombinant inbred line (RIL) population derived from the wild accession Ll-0 and the reference strain Landsberg (L), which show low and high stomatal abundance, respectively. Quantitative trait locus (QTL) analyses of stomatal index, stomatal density, and pavement cell density measured in the adaxial cotyledon epidermis, identified five loci. Three of the genomic regions affect all traits and were named () 1 to 3. is a large-effect QTL overlapping with (), the allele from L increasing all trait values. Additional analyses of natural and induced loss-of-function mutations in different genetic backgrounds revealed that dysfunctions have differential and opposite effects on the stomatal index in adaxial and abaxial cotyledon epidermis and confirmed that is the gene underlying . Ll-0 alleles at and displayed moderate and positive effects on the various traits. Furthermore, detailed developmental studies tracking primary and satellite stomatal lineages show that -Ll-0 allele promotes the spacing divisions that initiate satellite lineages, while the allele limits them. Finally, expression analyses suggest that and modulate satellization through partly different regulatory pathways. Our characterization of indicates that genetic modulation of satellization contributes to the variation for stomatal abundance in natural populations, and subsequently that this trait might be involved in plant adaptation.