Plant RelA/SpoT homolog confers salt tolerance in Escherichia coli and Saccharomyces cerevisiae.
To analyze the mechanisms of salt tolerance in the halophyte Suaeda japonica, Escherichia coli was used as a host organism to undertake functional screening of cDNAs encoding proteins that may play an important role for the salt-tolerance mechanisms. A transformant expressing RelA/SpoT homolog (Sj-RSH) was found to have enhanced salt tolerance. In E. coli, RelA/SpoT controlled the amount of guanosine tetraphosphate (ppGpp) and guanosine pentaphosphate (pppGpp), which are the effectors of the bacterial stringent response. Complementation analysis using the relA mutant of E. coli showed that Sj-RSH conferred the phenotype associated with (p)ppGpp synthesis. Furthermore, expression of Sj-RSH driven by the GAL1 promoter also gave rise to enhanced salt tolerance in yeast. Northern blot analyses of the yeast transformant revealed that the transcriptional levels of stress responsive genes including GPD1, VMA6, BMH1, HYP1 and HOG1 were clearly enhanced in the Sj-RSH transformant when compared with an empty vector transformant under stress-free and 1.5 M NaCl stress conditions. These results suggest that (p)ppGpp synthesis mediated by plant RelA/SpoT homologs plays a critical role for the transcriptional induction of several stress responsive genes, directly or indirectly in yeast, and that the conserved stress-resistance system may exist in higher plants.
Yamada
Akiyo
A
Department of Biotechnology, Faculty of Technology, Tokyo University of Agriculture and Technology, Naka-cho 2-24-16, Koganei, Tokyo, 184-8588 Japan. yamaden@cc.tuat.ac.jp
Tsutsumi
Kouichi
K
Tanimoto
Shizufumi
S
Ozeki
Yoshihiro
Y
D000222:Adaptation, Physiological / Q000187:drug effects / Q000235:genetics; D015152:Blotting, Northern; D019663:Chenopodiaceae / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D005816:Genetic Complementation Test; D006158:Guanosine Pentaphosphate / Q000378:metabolism; D006159:Guanosine Tetraphosphate / Q000378:metabolism; D008969:Molecular Sequence Data; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D011755:Pyrophosphatases / Q000235:genetics* / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D017422:Sequence Analysis, DNA; D012965:Sodium Chloride / Q000494:pharmacology
D018076:DNA, Complementary; D010940:Plant Proteins; D006159:Guanosine Tetraphosphate; D006158:Guanosine Pentaphosphate; D012965:Sodium Chloride; C027627:guanosine-3',5'-bis(diphosphate) 3'-pyrophosphatase; D011755:Pyrophosphatases