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.