The Arabidopsis Kinase-Associated Protein Phosphatase Regulates Adaptation to Na⁺ Stress

Abstract

The kinase-associated protein phosphatase (KAPP) is a regulator of the receptor-like kinase (RLK) signaling pathway. Loss-offunction 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 1 toxicity. The sensitivity to Na 1 is Ca 21 independent and is not due to altered intracellular K 1 /Na 1 . 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 1 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 1 stress. RLK pathway components, known to be modulated by NaCl at the messenger RNA level, are constitutively downregulated in rag1-1 mutant plants. The effect of NaCl on their expression is not altered by the rag1-1 mutation.Animal receptor Tyr kinases and receptor Ser/Thr kinases are cell surface enzyme-linked receptors that are activated by peptide ligands and initiate a diverse range of signal transduction pathways, including those that control cell growth, differentiation and survival, defensive responses. and metabolism (Holland and Holland, 2002). Receptor-like kinases (RLKs; a.k.a. plant receptor kinase; Cock et al., 2002) are animal receptor kinase orthologs in plants, so classified because of conserved structures that include an extracellular receptor, a transmembrane domain, and an intracellular kinase domain . The mechanisms by which RLKs activate and regulate downstream components of the signaling pathway resemble those of receptor Tyr kinases and receptor Ser/Thr kinases (Cock et al., 2002;. RLK activation occurs upon binding of an extracellular ligand to the plasma membrane-localized heterodimeric receptor form (Morris and Walker, 2003;Tichtinsky et al., 2003;Torii, 2004). Subsequently, the RLK complex undergoes autotransphosphorylation to form an active complex (Trotochaud et al., 1999(Trotochaud et al., , 2000Clark, 2001;Rojo et al., 2002). RLKs are also transcriptionally regulated (Becraft, 2002). Plant RLKs activate diverse signal transduction pathways, including those that control hormone responses Matsubayashi et al., 2002;Montoya et al., 2002;Scheer and Ryan, 2002;Yin et al., 2002;Szekeres, 2003), flower development (Williams et al., 1997;Stone et al., 1998), innate immunity against bacterial pathogens (Gomez-Gomez et al., 2001), self incompatibility (Braun et al., 1997), and root nodule formation (Downie and Walker, 1999;Endre et al., 2002;Krusell et al., 2002;Nishimura et al., 2002;Spaink, 2002;Stracke et al., 2002).The kinase-associated protein phosphatase (KAPP; Stone et al., 1994) is a cytosol...

Analysis of DNA methylation of maize in response to osmotic and salt stress based on methylation-sensitive amplified polymorphism

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Type 2C protein phosphatases in plants

“…Phenotypic and genetic studies indicate that KAPP controls plant adaptation to sodium salt stress. KAPP‐deficient plants are also impaired with respect to maintaining the proper balance of cell expansion and cell division [125].…”

SOS1 gene overexpression increased salt tolerance in transgenic tobacco by maintaining a higher K+/Na+ ratio

“…Toxic effects of Na + include inhibition of enzyme activity (Hasegawa et al, 2000) and disruption of K + nutrient acquisition (Zhu, 2003). Thus, it is essential for crops that cells must be able to transport or compartmentalize Na + to maintain non-toxic levels of cytosolic Na + (Manabe et al, 2008).…”