ABSTRACT
Cell number is an important determinant of final organ size. In the leaf, a large proportion of cells are derived from the stomatal lineage. Meristemoids, which are stem cell-like precursor cells, undergo asymmetric divisions, generating several pavement cells adjacent to the two guard cells. However, the mechanism controlling the asymmetric divisions of these stem cells prior to differentiation is not well understood. Here, we characterized PEAPOD (PPD) proteins, the only transcriptional regulators known to negatively regulate meristemoid division. PPD proteins interact with KIX8 and KIX9, which act as adaptor proteins for the corepressor TOPLESS. D3-type cyclin encoding genes were identified among direct targets of PPD2, being negatively regulated by PPDs and KIX8/9. Accordingly, kix8 kix9 mutants phenocopied PPD loss-of-function producing larger leaves resulting from increased meristemoid amplifying divisions. The identified conserved complex might be specific for leaf growth in the second dimension, since it is not present in Poaceae (grasses), which also lack the developmental program it controls.
Subject(s)
Arabidopsis Proteins/genetics , Arabidopsis/genetics , Multiprotein Complexes/genetics , Plant Leaves/genetics , Repressor Proteins/genetics , Transcription Factors/genetics , Adaptor Proteins, Signal Transducing/genetics , Adaptor Proteins, Signal Transducing/metabolism , Arabidopsis/growth & development , Arabidopsis/metabolism , Arabidopsis Proteins/metabolism , Binding Sites/genetics , Cyclin D3/genetics , Cyclin D3/metabolism , Gene Expression Regulation, Developmental , Gene Expression Regulation, Plant , Green Fluorescent Proteins/genetics , Green Fluorescent Proteins/metabolism , Microscopy, Confocal , Multiprotein Complexes/metabolism , Mutation , Phenotype , Plant Leaves/growth & development , Plant Leaves/metabolism , Plants, Genetically Modified , Protein Binding , Repressor Proteins/metabolism , Reverse Transcriptase Polymerase Chain Reaction , Transcription Factors/metabolismABSTRACT
Jasmonate (JA) signalling is mediated by the JASMONATE-ZIM DOMAIN (JAZ) repressor proteins, which are degraded upon JA perception to release downstream responses. The ZIM protein domain is characteristic of the larger TIFY protein family. It is currently unknown if the atypical member TIFY8 is involved in JA signalling. Here we show that the TIFY8 ZIM domain is functional and mediated interaction with PEAPOD proteins and NINJA. TIFY8 interacted with TOPLESS through NINJA and accordingly acted as a transcriptional repressor. TIFY8 expression was inversely correlated with JAZ expression during development and after infection with Pseudomonas syringae. Nevertheless, transgenic lines with altered TIFY8 expression did not show changes in JA sensitivity. Despite the functional ZIM domain, no interaction with JAZ proteins could be found. In contrast, TIFY8 was found in protein complexes involved in regulation of dephosphorylation, deubiquitination and O-linked N-acetylglucosamine modification suggesting an important role in nuclear signal transduction.