No abstract

The asymmetric cell divisions necessary for stomatal lineage initiation and progression in Arabidopsis () require the function of the basic helix-loop-helix (bHLH) transcription factor (). Mutants lacking do not produce stomata or lineages. Here, we isolated a new allele carrying a point mutation in the bHLH domain that displayed normal growth, but had an extremely low number of sometimes clustered stomata in the leaves, whereas the hypocotyls did not have any stomata. In vivo tracking of leaf epidermal cell divisions, combined with marker lines and genetic analysis, showed that the leaf phenotype is dosage dependent and results from the decreased ability to initiate and amplify lineages, defects in asymmetric cell fate allocation, and misorientation of asymmetric division planes. Notably, application of brassinosteroids (BRs) partly rescued the stomatal leaf phenotype of Transcriptomic analysis combining with BR treatments revealed that the expression of a set of SPCH target genes was restored by BRs. Our results also show that BR-dependent stomata formation and expression of some, but not all, SPCH target genes require the integrity of the bHLH domain of SPCH.

Highlights d BIN2 interacts with and phosphorylates PHGAPs d PHGAPs are enriched in the anticlinal face of the pavement cell indenting regions d BIN2 phosphorylation of PHGAPs affects their turnover and localization d Brassinosteroids activate ROP2 in the lobes through PHGAP degradation