The Arabidopsis salt overly sensitive 4 mutants uncover a critical role for vitamin B6 in plant salt tolerance.
Salt stress is a major environmental factor influencing plant growth and development. To identify salt tolerance determinants, a genetic screen for salt overly sensitive (sos) mutants was performed in Arabidopsis. We present here the characterization of sos4 mutants and the positional cloning of the SOS4 gene. sos4 mutant plants are hypersensitive to Na(+), K(+), and Li(+) ions. Under NaCl stress, sos4 plants accumulate more Na(+) and retain less K(+) compared with wild-type plants. SOS4 encodes a pyridoxal kinase that is involved in the biosynthesis of pyridoxal-5-phosphate, an active form of vitamin B6. The expression of SOS4 cDNAs complements an Escherichia coli mutant defective in pyridoxal kinase. Supplementation of pyridoxine but not pyridoxal in the growth medium can partially rescue the sos4 defect in salt tolerance. SOS4 is expressed ubiquitously in all plant tissues. As a result of alternative splicing, two transcripts are derived from the SOS4 gene, the relative abundance of which is modulated by development and environmental stresses. Besides being essential cofactors for numerous enzymes, as shown by pharmacological studies in animal cells, pyridoxal-5-phosphate and its derivatives are also ligands for P2X receptor ion channels. Our results demonstrate that pyridoxal kinase is a novel salt tolerance determinant important for the regulation of Na(+) and K(+) homeostasis in plants. We propose that pyridoxal-5-phosphate regulates Na(+) and K(+) homeostasis by modulating the activities of ion transporters.
Shi
Huazhong
H
Department of Plant Sciences, University of Arizona, Tucson, Arizona 85721, USA.
Xiong
Liming
L
Stevenson
Becky
B
Lu
Tiegang
T
Zhu
Jian-Kang
JK
D000222:Adaptation, Physiological / Q000187:drug effects; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D002586:Cesium / Q000494:pharmacology; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D008094:Lithium / Q000378:metabolism / Q000494:pharmacology; D008353:Mannitol / Q000494:pharmacology; D008969:Molecular Sequence Data; D009154:Mutation; D010802:Phylogeny; D018517:Plant Roots / Q000187:drug effects; D018520:Plant Shoots / Q000187:drug effects; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D011731:Pyridoxal Kinase / Q000235:genetics* / Q000378:metabolism; D011732:Pyridoxal Phosphate / Q000096:biosynthesis; D017386:Sequence Homology, Amino Acid; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology; D012965:Sodium Chloride / Q000494:pharmacology*; D025101:Vitamin B 6 / Q000502:physiology*; D014867:Water / Q000494:pharmacology
D029681:Arabidopsis Proteins; D014867:Water; D002586:Cesium; D008353:Mannitol; D012965:Sodium Chloride; D011732:Pyridoxal Phosphate; D025101:Vitamin B 6; D008094:Lithium; D012964:Sodium; D011731:Pyridoxal Kinase; D011188:Potassium