Towards genetic engineering drought stress tolerance in tropical maize using xerophyta viscosa peroxiredoxin 2 (Xvprx2) gene

Abstract

Drought has emerged as one of the major constraints to maize productivity causing devastating effects especially at flowering and grain filling stages. Recent work has shown that it is possible to confer drought tolerance to plants by using genes that code for the enzyme peroxiredoxin from the "resurrection" plant Xerophyta viscosa Baker [familyVelloziaceae]. Peroxiredoxin is an antioxidant that neutralizes excessive accumulation of ROS as result of drought stress. In this study two tropical maize varieties Katumani (KAT); an open pollinated (OPV) and Pwani Hybrid (PH) 01 were transformed for drought tolerance with a standard binary vector containing the XvPrx2 gene mobilized in the Agrobacterium tumefaciens strain EHA 101. The bar selectable marker gene located within T-DNA region together with the gene of interest was used to select for transformed events under medium containing bialaphos. Transformation frequencies (TFs) for KAT and PHO 1 varieties using XvPrx2 gene averaged at 26.4% and 3.8% respectively. Embryo necrosis was seen to be a major problem following infection especially in PHOI compromising TF. The different TFs for PHO1 and KAT could be as a result of differences in genotype hypersensitivity to Agrobacterium infection. This suggests that genotype is an important factor to be considered in transformation experiments. Inclusion of L-cysteine at levels tested (0, 100, 200, and 300 mg/L) was observed to significantly (P<0.5) improve the survival ability of PHO1 (P<0.001) but slowed or inhibited the embryo ability to form callus. Cell death and failure in proliferation of type II calli in regeneration stage was observed and could be attributed to the use of cefotaxime for Agrobacterium suppression as has been suggested by some previous reports. It was possible for KAT to be regenerated to putative transgenic maize plants with RF of 6.7%. However, PH 01 could not be regenerated and thus no putative transgenic plants were obtained from this variety. This is because all calli of this variety died in the REGII medium. Since the gene has only been tested in Digitaria sanguinalis and Arabdopsis thaliana and not in any other commercial crop, to my knowledge, this work represent the first report on genetic transformation of Tropical maize varieties with the XvPrx2 gene through Agrobacterium tumefaciens-mediated standard binary vector technique. The method is efficient and reproducible and could be applied to other lines for production of fertile genetically transformed maize.