A gene encoding proline dehydrogenase is not only induced by proline and hypoosmolarity, but is also developmentally regulated in the reproductive organs of Arabidopsis

The cDNA clone ERD5 (early responsive to dehydration), isolated from l-h-de hydrated Arabidopsis, encodes a precursor of proline (Pro) dehydrogenase (P roDH), which is a mitochondrial enzyme involved in the first step of the co nversion of Pro to glutamic acid. The transcript of the erd5 (ProDH) gene w as undetectable when plants were dehydrated, but large amounts of transcrip t accumulated when plants were subsequently rehydrated. Accumulation of the transcript was also observed in plants that had been incubated under hypoo smotic conditions in media that contained L- or D-Pro. We isolated a 1.4-kb DNA fragment of the putative promoter region of the ProDH gene. The beta-g lucuronidase (GUS) reporter gene driven by the 1.4-kb ProDH promoter was in duced not only by rehydration but also by hypoosmolarity and L- and D-Pro a t significant levels in transgenic Arabidopsis plants. The promoter of the ProDH gene directs strong GUS activity in reproductive organs such as polle n and pistils and in the seeds of the transgenic plants. GUS activity was d etected in vegetative tissues such as veins of leaves and root tips when th e transgenic plants were exposed to hypoosmolarity and Pro solutions. GUS a ctivity increased during germination of the transgenic plants under hypoosm olarity. The relationship between Pro metabolism and the physiological aspe cts of stress response and development are discussed.