Plant Genome IV Conference Plant Genome IV Conference
Progressive water deficit alterations are known to change the
expression of many genes in plants. Recent research has focussed
primarily on dessication-induced genes like the lea-genes which have
been characterized in detail. However the large variability of drought
response in species and particulary variety-specific tolerances or
adaptions are hardly understood at the molecular level. Drought
tolerance is supposed to be a polygenic trait. It is expected that the
differences in the expression levels of drought-stress associated
genes are partially responsible for quantitative variations of drought
response traits. These cDNAs may be regarded as "candidate" genes
contributing to drought-tolerance and could therefore be used for QTL
analysis. We have started with the isolation of a comprehensive set
of cDNAs whose mRNAs show altered expression as a result of water
deficit gradients which range from a moderate to severe drought-stress
in young maize plants. To date differential screening of a leaf cDNA
library yielded about 15 putative drought-stress related cDNAs which
have been characterized by sequencing and with northern hybridization
techniques. The identified cDNAs belong to the highly abundant hsp70s,
ubiquitines, proline-rich and phospholipid transfer proteins,
alpha-tubulines, lipoxygenases, "seed imbibition" protein and
ABA/fruit ripening homologue proteins. Five to ten times more of the
corresponding mRNAs for the majority of these cDNAs accumulate
preferentially in green leaves under conditions of moderate
drought-stress when compared with normal plants. A few cDNAs are
selectively induced under conditions of more severe drought-stress.
For a more complete investigation of drought associated cDNAs,
including those with lower abundance, shoot- and root-cDNA libraries
are presently screened by subtractive hybridization techniques.
(This investigation is part of Network B3 of the PTP project supported
by the European Union)