Mitogen-activated protein kinase 6 controls root growth in Arabidopsis by modulating Ca2+-based Na+ flux in root cell under salt stress

• Published in: Journal of plant physiology 2014-03, Vol.171 (5), p.26-34
• Main Authors: Han, Shuan, Wang, Chi-wen, Wang, Wen-le, Jiang, Jing
• Format: Article
• Language: English
• Subjects: Arabidopsis; Arabidopsis - drug effects; Arabidopsis - genetics; Arabidopsis - growth & development; Arabidopsis - physiology; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Ca2; Calcium - metabolism; Cytosol - metabolism; Elongation; Flux; Gene Expression Regulation, Plant; Homeostasis; Inhibitors; Kinases; Membranes; Mitogen-Activated Protein Kinases - genetics; Mitogen-Activated Protein Kinases - metabolism; Molecular Sequence Data; mpk6; Mutation; Na+ flux; NaCl; Plant Roots - drug effects; Plant Roots - genetics; Plant Roots - growth & development; Plant Roots - physiology; Potassium - metabolism; Proteins; Reverse Transcriptase Polymerase Chain Reaction; Root growth; Roots; Seedlings - genetics; Seedlings - growth & development; Seedlings - physiology; Sodium - metabolism; Sodium Chloride - pharmacology; Stress, Physiological - drug effects; Toxicity
• ISSN: 0176-1617; 1618-1328
• DOI: 10.1016/j.jplph.2013.09.023

Little is known about the role of mitogen-activated protein kinase 6 (MPK6) in Na+ toxicity and inhibition of root growth in Arabidopsis under NaCl stress. In this study, we found that root elongation in seedlings of the loss-of-function mutants mpk6-2 and mpk6-3 was less sensitive to NaCl or Na-glutamate, but not to KCl or mannitol, as compared with that of wild-type (WT) seedlings. The less sensitive characteristic was eliminated by adding the Ca2+ chelator EGTA or the Ca2+ channel inhibitor LaCl3, but not the Ca2+ ionophore A23187. This suggested that the tolerance of mpk6 to Na+ toxicity was Ca2+-dependent. We measured plasma membrane (PM) Na+-conducted currents (NCCs) in root cells. Increased concentrations of NaCl increased the inward NCCs while decreased the outward NCCs in WT root cells, attended by a positive shift in membrane potential. In mpk6 root cells, NaCl significantly increased outward but not inward NCCs, accompanied by a negative shift in membrane potential. That is, mpk6 decreased NaCl-induced the Na+ accumulation by modifying PM Na+ flux in root cells. Observations of aequorin luminescence revealed a NaCl-induced increase of cytosolic Ca2+ in mpk6 root cells, resulting from PM Ca2+ influx. An increase of cytosolic Ca2+ was required to alleviate the NaCl-increased Na+ content and Na+/K+ ratio in mpk6 roots. Together, these results show that mpk6 accumulated less Na+ in response to NaCl because of the increased cytosolic Ca2+ level in root cells; thus, its root elongation was less inhibited than that of WT by NaCl.