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Abiotic-Stress Home

Development of drought-tolerant maize by genetic modification

J.A. Thomson, S.G. Mundree

Drought is one of the most serious abiotic stresses affecting crops in Africa. Our group has been addressing the problem using genes obtained from the resurrection plant, Xerophyta viscosa. This South African indigenous monocot, which grows in cracks in rocks in the Drakensberg Range, can tolerate losses of up to 95% relative water content. Upon rehydration, it can ‘resurrect’ within 72 hours. At the last Rockefeller Foundation meeting we reported on the protection afforded to transgenic plants of XvSAP1, which encodes a unique membrane-binding protein. At this meeting we report on the abiotic stress protection afforded by XvAR, encoding an aldose reductase protein that converts glucose to the osmoprotectant sorbitol. In addition we present data on two genes encoding antioxidant proteins. XvPer1 codes for a 1Cys-peroxiredoxin that is induced, at both RNA and protein levels, by dehydration, heat, high light intensity and salt. It has a nuclear localization signal and has been shown to be located in the nucleus. XvPer1 has been compared with its closest Arabidopsis thaliana orthologue and has been found to be unique in that the latter, like all other 1Cys-peroxiredoxins, is only found in seeds, while XvPer1 is found in vegetative tissue. Transgenic Digitaria sanguinalis and maize plants carrying this gene are being tested for abiotic stress tolerance. XvPrx2 encodes a type II peroxiredoxin that is induced by dehydration, low temperature and abscisic acid (ABA). Unlike most type II Prx’s, this protein possesses only one Cys residue. A point mutation introducing the second one showed no increase in activity, again showing the uniqueness of X. viscosa peroxiredoxins. Finally, as transgenic maize plants constitutively expressing genes for drought tolerance are unlikely to be healthy under normal conditions, we have cloned the promoters of both XvSAP1 and XvPer1. These have been fused to the luciferase indicator gene and are being tested in transgenic plants.

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