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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

The Arabidopsis Kinase-Associated Protein Phosphatase Regulates Adaptation to Na⁺ Stress^[C]

Center for Plant Environmental Stress Physiology, Purdue University, West Lafayette, Indiana 47907–2010 (Y.M., R.A.B., F.L., I.S.); Department of Horticultural Sciences, Texas A&M University, College Station, Texas 77843–2133 (H.K.); State Key Laboratory of Plant Cell and Chromosome Engineering, Center for Agricultural Resources, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Shijiazhuang, Hebei 050021, China (T.W., X.L.); and Department of Agricultural Engineering and Agronomy, University of Naples Federico II, Portici 80055, Italy (A.M.)

The kinase-associated protein phosphatase (KAPP) is a regulator of the receptor-like kinase (RLK) signaling pathway. Loss-of-function mutations rag1-1 (root attenuated growth1-1) and rag1-2, in the locus encoding KAPP, cause NaCl hypersensitivity in Arabidopsis thaliana. The NaCl hypersensitive phenotype exhibited by rag1 seedlings includes reduced shoot and primary root growth, root tip swelling, and increased lateral root formation. The phenotype exhibited by rag1-1 seedlings is associated with a specific response to Na⁺ toxicity. The sensitivity to Na⁺ is Ca²⁺ independent and is not due to altered intracellular K⁺/Na⁺. Analysis of the genetic interaction between rag1-1 and salt overly sensitive1 (sos1-14) revealed that KAPP is not a component of the SOS signal transduction pathway, the only Na⁺ homeostasis signaling pathway identified so far in plants. All together, these results implicate KAPP as a functional component of the RLK signaling pathway, which also mediates adaptation to Na⁺ stress. RLK pathway components, known to be modulated by NaCl at the messenger RNA level, are constitutively down-regulated in rag1-1 mutant plants. The effect of NaCl on their expression is not altered by the rag1-1 mutation.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Albino Maggio (albino.maggio{at}unina.it).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.109009

^* Corresponding author; e-mail albino.maggio{at}unina.it.

Received September 13, 2007; accepted December 13, 2007; published December 27, 2007.