The Role of HEAT SHOCK PROTEIN 70-1 in the Regulation of Plant Growth

Plants continuously modify their morphogenetic program in response to environmental signals. Modification of plant growth is obtained in part by modulating the turgor pressure, the driving force of cell expansion, and by remodeling of plant cell wall composition and structure. The receptor-like kinases FEI1 and FEI2 are required for proper root growth under restrictive conditions of high-salt or high-sucrose concentrations. Genetic screen for downstream elements in the FEI-pathway identified three independent HEAT SHOCK PROTIEN 70-1 (HSP70-1) alleles as suppressors of the fei1fei2 short and swollen root phenotype. Moreover, these alleles, named hsp70-1^shou5, suppress also other fei1fei2 phenotypes like, the swollen hypocotyl of dark-grown seedlings and mal-organized seed mucilage. HSP70s are highly conserved ATP-driven chaperones encoded by enlarged gene families in plants. So far, functional analysis of HSP70 proteins was restricted by high levels of functional redundancy and the lack of HSP70-specific inhibitors. The data presented demonstrate that HSP70-1 function is required for root growth arrest in fei1fei2 background. Interestingly, while hsp70-1 loss-of-function allele (SLAK_135531) was unable to suppress the fei1fei2 phenotypes, the dominant-interfering hsp70-1^shou5 alleles overcome functional redundancy and uncover a new role for HSP70-1 in growth regulation. Recent studies suggest that HSP70 functions, as part of a protein complex with HSP90 and SGT1b, in the regulation of plant E3-ligase mediated hormone signal transduction in response to various environmental signals like high temperature. In order to further investigate the HSP70-mediated machinery employed in growth regulation in response to different environmental cues, transgenic plants expressing FLAG-tagged form of either HSP70-1^shou5 or the HSP70-1^WT were generated. Using blue native gel electrophoresis, HSP70-1 was identified as part of about 500KDa protein complex. Immuno-precipitation followed by mass spectrometry will be used to elucidate the co-chaperons and HSP70-1 target-proteins involved in growth regulation as part of plant adaptation to changing environment.