Over-expression of an ABA Biosynthesis Gene (NCED) with a Stress-inducible Promoter Improves Drought Tolerance in Petunia (Petunia xhybrida)

Drought stress during shipping and retail reduces the postproduction quality, marketability and shelf life of potted and bedding plants. Plant hormone abscisic acid (ABA) plays an important role in the regulation of stomatal aperture, and is therefore a key hormone in the plant’s response to water stress. One of the key regulatory steps in ABA biosynthesis is the cleavage reaction of a 9-cis-epoxy-carotenoid catalyzed by 9-cis-epoxy-carotenoid dioxygenases (NCED). Over-expression of NCED using the constitutive promoter 35S resulted in enhanced accumulation of ABA, accompanied by stomatal closure and increased water use efficiency (WUE). However, the negative effects were observed including increased seed dormancy, delayed germination and stunted growth. Here, to reduce the risk of such pleiotropic effects, we generated transgenic petunia plants containing NCED coding region under the control of a stress-inducible promoter. We used some of the T1 plants to conduct a preliminary drought assay. Under non-stress conditions, transgenic plants displayed normal growth, and were indistinguishable from control plants.  Under stress conditions, transgenic plants grown without irrigation showed dramatically delayed wilting than all control plants. Results from our preliminary drought assay indicate overexpression of a key ABA biosynthesis gene driven by a stress-inducible promoter provides strong protection against severe drought stress.