PETAL LOSS, a trihelix transcription factor that represses growth in Arabidopsis thaliana, binds the energy-sensing SnRK1 kinase AKIN10

Abstract Organogenesis in plants involves differential growth. Rapidly growing primordia are distinguished from the meristem and each other by slower growing boundaries. PETAL LOSS (PTL) is a trihelix transcription factor of Arabidopsis that represses growth in boundaries between newly arising sepals. To identify partners involved in this growth limitation, a young inflorescence cDNA library was screened by yeast two-hybrid technology with PTL as bait. The most frequent prey identified was AKIN10, the catalytic α-subunit of the Snf1-related kinase1 (SnRK1). Interaction was mapped to the C-terminal (non-kinase) half of AKIN10 and the N-terminal portion of PTL. Binding of PTL was specific to AKIN10 as there was little binding to the related AKIN11. The interaction was confirmed by co-immunoprecipitation in vitro . Fluorescently tagged products of 35S:YFP-AKIN10 and 35S:CFP–PTL also interacted when transiently expressed together in leaf cells of Nicotiana benthamiana . In this case, most of the cytoplasmic AKIN10 was preferentially moved to the nucleus where PTL accumulated, possibly because a nuclear export sequence in AKIN10 was now masked. During these experiments, we observed that AKIN10 could variably accumulate in the Golgi, shown by its co-localization with a tagged Golgi marker and through its dispersal by brefeldin A. Tests of phosphorylation of PTL by AKIN10 gave negative results. The functional significance of the PTL–AKIN10 interaction remains open, although a testable hypothesis is that AKIN10 senses lower energy levels in inter-sepal zones and, in association with PTL, promotes reduced cell division.Key words: