Tomato stomatal development: diverse mechanisms of adaptive flexibility revealed by multi-species analysis

Ido Nir
The Institute of Plant Sciences, ARO, Volcani Center, HaMaccabbim Road 68, POB 15159, Rishon LeZion 7505101, Israel.

The bHLH transcription factor SPEECHLESS (SPCH) is thought to be a critical target for environmental inputs into stomatal development. Despite the power of Arabidopsis as a model for stomatal development, we found that crop plants like tomatoes often rely on different cellular and genetic strategies to achieve optimal stomatal distributions. By creating genetically encoded reporters of the stomatal lineage and using long-term confocal microscopy, we tracked the developing epidermis of M82 (WT) and mutant tomato seedlings. We found that, like in Arabidopsis, tomato undergoes a series of asymmetric and symmetric cell divisions to produce stomata. However, we found one type of asymmetric division (ACD) was missing in the tomato epidermis, and other ACDs could be used to generate non-stomatal cells. These data suggest differences in ACD strategies that control stomatal production between plant species. Since SPCH integrates environmental information in stomatal development, we targeted the tomato SPCH promoter for CRISPR-based mutagenesis. By screening lines in response to light, temperature, and drought, we identified putative SPCH cis-regulatory elements that indicate complexity in the regulation of developmental flexibility. Taken together, these results further our understanding of the species-specific cellular and genetic pathways that plants use to adapt to their environment.