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Plant Physiol, February 2000, Vol. 122, pp. 357-368
Hypersensitivity of an Arabidopsis Sugar Signaling Mutant toward
Exogenous Proline Application1
Hanjo
Hellmann,2
Dietmar
Funck,2
Doris
Rentsch, and
Wolf B.
Frommer*
Pflanzenphysiologie, Zentrum für Molekularbiologie der
Pflanzen, Universität Tübingen, D-72076
Tübingen, Germany.
In
transgenic Arabidopsis a patatin class I promoter from potato is
regulated by sugars and proline (Pro), thus integrating signals derived
from carbon and nitrogen metabolism. In both cases a signaling cascade
involving protein phosphatases is involved in induction. Other
endogenous genes are also regulated by both Pro and carbohydrates.
Chalcone synthase (CHS) gene expression is induced by both, whereas the
Pro biosynthetic  1-pyrroline-5-carboxylate synthetase
(P5CS) is induced by high Suc concentrations but repressed by Pro, and
Pro dehydrogenase (ProDH) is inversely regulated. The mutant
rsr1-1, impaired in sugar dependent induction of the
patatin promoter, is hypersensitive to low levels of external Pro and
develops autofluorescence and necroses. Toxicity of Pro can be
ameliorated by salt stress and exogenously supplied metabolizable
carbohydrates. The rsr1-1 mutant shows a reduced
response regarding sugar induction of CHS and P5CS expression. ProDH expression is
de-repressed in the mutant but still down-regulated by sugar. Pro
toxicity seems to be mediated by the degradation intermediate
1-pyrroline-5-carboxylate. Induction of the patatin
promoter by carbohydrates and Pro, together with the Pro
hypersensitivity of the mutant rsr1-1, demonstrate a new
link between carbon/nitrogen and stress responses.
1
This research was financially supported by
the Deutsche Forschungsgemeinschaft (contract no. FR989/4-2) and by
the European Community CARBGEN project (contract no.
BIO4-CT96-0311).
2
These authors contributed equally to the paper.
*
Corresponding author; e-mail frommer{at}uni-tuebingen.de; fax
49-7071-29-3287.
© 2000 American Society of Plant Physiologists
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