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Mol Plant. 2014 Apr;7(4):722-38. doi: 10.1093/mp/sst157. Epub 2013 Nov 8.

Salt stress in Arabidopsis: lipid transfer protein AZI1 and its control by mitogen-activated protein kinase MPK3.

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Department of Applied Genetics and Cell Biology, University of Natural Resources and Life Sciences, Muthgasse 18, 1190 Vienna, Austria.


A plant's capability to cope with environmental challenges largely relies on signal transmission through mitogen-activated protein kinase (MAPK) cascades. In Arabidopsis thaliana, MPK3 is particularly strongly associated with numerous abiotic and biotic stress responses. Identification of MPK3 substrates is a milestone towards improving stress resistance in plants. Here, we characterize AZI1, a lipid transfer protein (LTP)-related hybrid proline-rich protein (HyPRP), as a novel target of MPK3. AZI1 is phosphorylated by MPK3 in vitro. As documented by co-immunoprecipitation and bimolecular fluorescence complementation experiments, AZI1 interacts with MPK3 to form protein complexes in planta. Furthermore, null mutants of azi1 are hypersensitive to salt stress, while AZI1-overexpressing lines are markedly more tolerant. AZI1 overexpression in the mpk3 genetic background partially alleviates the salt-hypersensitive phenotype of this mutant, but functional MPK3 appears to be required for the full extent of AZI1-conferred robustness. Notably, this robustness does not come at the expense of normal development. Immunoblot and RT-PCR data point to a role of MPK3 as positive regulator of AZI1 abundance.


AZI1; Arabidopsis; MAPK; MPK3; in vivo interaction.; lipid transfer protein; phosphorylation; salt stress

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