Water Use and Drought Response in Cultivated and Wild Apples - Abiotic Stress: Plant Responses and Applications in Agriculture - page 259

10.1. Status and results
Analysis of 'Royal Gala' response to a simulated moderate-severe drought: Clonally
replicated individuals growing on their own roots were generated for the suppression
subtractive hybridization experiments. We identified several hundred different genes up-
regulated or down-regulated in roots, bark and leaves when DNA from drought-treated
tissues served as 'tester' and DNA from well watered controls acted as 'driver' (10-fold higher
amount). Some genes unique to our experiments that increased in response to drought are
shown in Table 2. A number of drought-responsive genes were common to genes isolated from
other plants systems, both dicot and monocot. Figures 2-4 show the relative expression of some
of the common and unique genes in apple roots, bark and leaves.
Most of the genes examined regardless of tissue origin showed around a two-fold difference
between watered and water-deficit treaments. A few genes were substanitally up-regulated
in response to drought. including the auxin-induced gene from leaves (8-fold increase) and
asparagine synthase from bark (4-fold increase). A few genes in roots were also significantly
up-regulated in response to drought treatment, one of which was NPR1 (3-fold increase;
manuscript submitted). From this information, including the expression of genes not shown
here, we have generated a list of potential up-regulated genes responding to a relatively long
term drought that can be used to determine if there is any correlation of expression in M.
sieversii lines with high and low WUE values.
10.2. Promoter comparison of NRT2.4 from apple, peach and Arabidopsis
A high affinity nitrate transporter gene from the 'Royal Gala' root SSH library (see Table 2)
was shown by RT-qPCR to be elevated in roots and bark in response to drought treatment
(manuscript submitted). Approximately 700 bp upstream of the ATG start codon was obtained
from the genomic sequence of 'Golden Delicious' (Genome Database for Rosaceae; http://
www.rosaceae.org/). Several cis -elements associated with tissue specificity or stress response
were identified. To identify elements preserved during evolution, promoter regions from
peach NRT2.4 and an Arabidopsis AtNRT2.4 gene were analyzed for comparison (Figure 5).
All three genes contained consensus, well defined TATA boxes within 80-100 bp of the
translation start. A number of MYB and MYC binding sites were identified in similar positions
in all three promoters. The peach promoter was missing a root-specific element seen in both
MdNRT2.4 and AtNRT2.4. Interestingly, both the apple and peach promoters contained a
drought responsive element on the reverse strand. Overall the elements identified in the apple
NRT2.4 promoter are consistent with the expression analysis results.
Screening the M. sieversii population at site 6 in Kazakhstan: A core diversity population of
M. sieversii trees (34 individuals representing 14 sibling groups) collected from Kazakhstan site
6 and maintained as seedlings at the Geneva, NY ARS Plant Genetic Resources Unit, was
sampled for stable carbon isotope discrimination to select individuals with extreme values
compared to 'Royal Gala'. The results are shown in Figure 6. Two individuals from each end
of the WUE spectrum were chosen for further characterization.