Expression of apoplastically secreted tobacco osmotin in cotton confers drought tolerance
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abstract
Osmotin or osmotin-like proteins have been shown to be induced in several plant species in response to various types of biotic and abiotic challenges. The protein is generally believed to be involved in protecting the plant against these stresses. Although some understanding of the possible mechanism underlying the defense function of osmotin against biotic stresses is beginning to emerge, its role in abiotic stress response is far from clear. We have transformed cotton plants with a tobacco-osmotin gene, lacking the sequence encoding its 20 amino acid-long, C-terminal vacuolar-sorting motif, under the control of CaMV 35S promoter. Apoplastic secretion of the recombinant protein was confirmed and the plants were evaluated for their ability to tolerate drought conditions. Under polyethylene glycol-mediated water stress, the osmotin-expressing seedlings showed better growth performance. The transformants showed a slower rate of wilting during drought and faster recovery following the termination of dry conditions in a greenhouse setting. During drought, the leaves from transgenic plants had higher relative water content and proline levels, while showing reduced H2O2 levels, lipid peroxidation and electrolyte leakage. Importantly, following a series of dry periods, the osmotin transformants performed better in terms of most growth and developmental parameters tested. Most relevant, the fiber yield of transgenic plants did not suffer as much as that of their non-transgenic counterparts under drought conditions. The results provide direct support for a protective role of osmotin in cotton plants experiencing water stress and suggest a possible way to achieve tolerance to drought conditions by means of genetic engineering. 2009 Springer Science+Business Media B.V.
