RESUMO
In Arabidopsis roots, some epidermal cells differentiate into root hair cells. Auxin regulates root hair positioning, while ethylene controls cell elongation. Phyllobacterium brassicacearum STM196, a beneficial strain of plant growth promoting rhizobacteria (PGPR) isolated from the roots of field-grown oilseed rape, stimulates root hair elongation in Arabidopsis thaliana seedlings. We investigated the role of ethylene in the response of root hair cells to STM196 inoculation. While we could not detect a significant increase in ethylene biosynthesis, we could detect a slight activation of the ethylene signalling pathway. Consistent with this, an exhaustive survey of the root hair elongation response of mutants and transgenic lines affected in the ethylene pathway showed contrasting root hair sensitivities to STM196. We propose that local ethylene emission contributes to STM196-induceed root hair elongation.
Assuntos
Arabidopsis/crescimento & desenvolvimento , Arabidopsis/microbiologia , Etilenos/metabolismo , Phyllobacteriaceae/fisiologia , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/microbiologia , Transdução de Sinais , Arabidopsis/efeitos dos fármacos , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Etilenos/farmacologia , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Genótipo , Ácidos Indolacéticos/metabolismo , Mutação/genética , Phyllobacteriaceae/efeitos dos fármacos , Raízes de Plantas/efeitos dos fármacos , Raízes de Plantas/genética , Estabilidade Proteica/efeitos dos fármacos , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Plântula/efeitos dos fármacos , Plântula/genética , Plântula/crescimento & desenvolvimento , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/genéticaRESUMO
Programmed cell death (PCD) has a key role in defence and development of all multicellular organisms. In plants, there is a large gap in our knowledge of the molecular machinery involved at the various stages of PCD, especially the early steps. Here, we identify kiss of death (KOD) encoding a 25-amino-acid peptide that activates a PCD pathway in Arabidopsis thaliana. Two mutant alleles of KOD exhibited a reduced PCD of the suspensor, a single file of cells that support embryo development, and a reduced PCD of root hairs after a 55°C heat shock. KOD expression was found to be inducible by biotic and abiotic stresses. Furthermore, KOD expression was sufficient to cause death in leaves or seedlings and to activate caspase-like activities. In addition, KOD-induced PCD required light in leaves and was repressed by the PCD-suppressor genes AtBax inhibitor 1 and p35. KOD expression resulted in depolarization of the mitochondrial membrane, placing KOD above mitochondria dysfunction, an early step in plant PCD. A KODâ·GFP fusion, however, localized in the cytosol of cells and not mitochondria.