Antisense expression of an Arabidopsis omega-3 fatty acid desaturase gene reduces salt/drought tolerance in transgenic tobacco plants

A wound-inducible Arabidopsis plastid omega-3 fatty acid desaturase (fad7) cDNA was obtained. Transgenic tobacco plants were produced by integration of the antisense fad7 DNA fragments under the control of a CaMV 35S promoter into the genome. Two transgenic T1 lines, AsFAD714 and 716, showed a strong expression of the antisensefad7 and reduced amounts of linolenic acid compared with the control plants. The two T1 lines were highly sensitive to dehydration conditions, showing growth retardation on the MS medium in the presence of 250 mM NaCl, and severe wilting under drought conditions. The expression of the transcriptional factor gene abf4 transducing ABA-dependent signal in response to drought stress was strongly induced in the control plants, but far less in the AsFAD716 line. This suggests that the inhibitory effect of the antisense fad7 gene expression on the ABF-mediated stress-responsive gene regulation may reduce drought tolerance in the AsFAD716 line. However, no significant difference in the ABA concentration was found between the control and the AsFAD716 line under normal and drought conditions.