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bioRxiv · 10.1101/2021.02.02.429361

A novel positive feedback mechanism of ABI5 phosphorylation by mitogen activated protein kinase-3 regulates ABA signaling in Arabidopsis

Bhagat, P. K.·Verma, D.·Verma, N.·Sinha, A. K.
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Abstract

Seed germination is the crucial physiological process regulated by both environmental and endogenous phytohormones. ABA negatively regulates seed germination, post-germination growth and floral transition, however, the cross talk between multiple regulatory pathways are still unclear. Here, we show that ABA activates two MAP kinases, AtMPK3/AtMPK6 and selectively regulates the transcript of AtMPK3 through ABI5, a master regulator of ABA signaling. As a feedback loop, AtMPK3 interacts and phosphorylates ABI5 at the serine-314 position. ABI5 phosphorylation by MAP kinases positively regulates ABI5 nuclear localization and negatively regulates its dimerization. Subcellular localization of ABI5 phospho-null protein further suggests the role of phosphorylation in regulation of its cytoplasmic stability and its nuclear dimerization. Overexpression of phosphor-null ABI5 in abi5-8 mutant restored the ABA sensitivity during seed germination and delayed the floral transition as compared to phospho-mimic ABI5. Additionally, overexpression of constitutive phosphorylated ABI5 in abi5-8 mutants suggest that phosphorylation makes ABI5 partially inactive. Furthermore, phospho-null ABI5 plants showed drought sensitive phenotype whereas, mpk3, mkk4, mkk5, abi5-8 and phosphor-mimic plants showed drought tolerant phenotype. Our findings present a new insight between MAP kinase cascade and ABA signaling which collectively regulates the ABA response through ABI5 phosphorylation.

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Bhagat, P. K., Verma, D., Verma, N., Sinha, A. K.. 2021-02-02. A novel positive feedback mechanism of ABI5 phosphorylation by mitogen activated protein kinase-3 regulates ABA signaling in Arabidopsis. https://doi.org/10.1101/2021.02.02.429361

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