Mitogen-activated protein kinase 6 controls root growth in Arabidopsis by modulating Ca2+ -based Na+ flux in root cell under salt stress.
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 Ca(2+) chelator EGTA or the Ca(2+) channel inhibitor LaCl3, but not the Ca(2+) ionophore A23187. This suggested that the tolerance of mpk6 to Na(+) toxicity was Ca(2+)-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 Ca(2+) in mpk6 root cells, resulting from PM Ca(2+) influx. An increase of cytosolic Ca(2+) 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 Ca(2+) level in root cells; thus, its root elongation was less inhibited than that of WT by NaCl.
State Key Laboratory of Cotton Biology, Key Laboratory of Plant Stress Biology, College of Life Sciences, Henan University, Kaifeng 475004, People's Republic of China.
Shuan
S
Han
State Key Laboratory of Cotton Biology, Key Laboratory of Plant Stress Biology, College of Life Sciences, Henan University, Kaifeng 475004, People's Republic of China.
Chi-wen
CW
Wang
State Key Laboratory of Cotton Biology, Key Laboratory of Plant Stress Biology, College of Life Sciences, Henan University, Kaifeng 475004, People's Republic of China.
Wen-le
WL
Wang
State Key Laboratory of Cotton Biology, Key Laboratory of Plant Stress Biology, College of Life Sciences, Henan University, Kaifeng 475004, People's Republic of China. Electronic address: jiangjing@henu.edu.cn.
Jing
J
Jiang
D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D006706:Homeostasis; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D011188:Potassium / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D036226:Seedlings / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D012964:Sodium / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology*; D013312:Stress, Physiological / Q000187:drug effects
D029681:Arabidopsis Proteins; D012965:Sodium Chloride; D012964:Sodium; C436293:MPK6 protein, Arabidopsis; D020928:Mitogen-Activated Protein Kinases; D011188:Potassium; D002118:Calcium
Ca(2+); Na(+) flux; NaCl; Root growth; mpk6