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Letters to Nature

Nature 418, 793-797 (15 August 2002) | doi:10.1038/nature00936; Received 22 April 2002; Accepted 14 June 2002

Modulation of an RNA-binding protein by abscisic-acid-activated protein kinase

Jiaxu Li1,2, Toshinori Kinoshita3, Sona Pandey1, Carl K.-Y. Ng1, Steven P. Gygi4, Ken-ichiro Shimazaki3 & Sarah M. Assmann1

  1. Biology Department, The Pennsylvania State University, 208 Mueller Laboratory, University Park, Pennsylvania 16802, USA
  2. Department of Biology, Faculty of Science, Kyushu University, Ropponmatsu, Fukuoka 810-8560, Japan
  3. Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA
  4. Present address: Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.

Correspondence to: Jiaxu Li1,2Sarah M. Assmann1 Correspondence should be addressed to J.L. (e-mail: Email: jiaxu_li@hms.harvard.edu) or S.M.A. (e-mail: Email: sma3@psu.edu). Requests for materials should be addressed to S.M.A. The sequence of the AKIP1 cDNA has been deposited in GenBank, accession no. AF403292.

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Protein kinases are involved in stress signalling in both plant and animal systems. The hormone abscisic acid mediates the responses of plants to stresses such as drought, salinity and cold. Abscisic-acid-activated protein kinase (AAPK)—found in guard cells, which control stomatal pores—has been shown to regulate plasma membrane ion channels1. Here we show that AAPK-interacting protein 1 (AKIP1), with sequence homology to heterogeneous nuclear RNA-binding protein A/B, is a substrate of AAPK. AAPK-dependent phosphorylation is required for the interaction of AKIP1 with messenger RNA that encodes dehydrin, a protein implicated in cell protection under stress conditions. AAPK and AKIP1 are present in the guard-cell nucleus, and in vivo treatment of such cells with abscisic acid enhances the partitioning of AKIP1 into subnuclear foci which are reminiscent of nuclear speckles. These results show that phosphorylation-regulated RNA target discrimination by heterogeneous nuclear RNA-binding proteins2 may be a general phenomenon in eukaryotes, and implicate a plant hormone in the regulation of protein dynamics during rapid subnuclear reorganization.