3.5 Expression of one-third of drought-responsive genes was not
affected by Fld presence
Clustering of DE transcripts allows identification of gene groups that
display similar expression patterns and presumably share common
regulatory pathways. Total leaf transcripts detected in our microarray
were thus grouped into 47 clusters of widely different size. The most
highly populated one (27622 members, corresponding to
~85% of all leaf-expressed genes) included those
transcripts whose levels were not affected by treatment or genotype. Of
the remaining 46 clusters containing genes differentially expressed in
response to water limitation and/or Fld presence (4847 DE genes), we
focused in 17 clusters that were either highly populated or enriched in
pathways and functional categories associated to stress responses, redox
biochemistry and chloroplast functions, comparing vis-à-vis those
that exhibit contrasting expression behaviors (e.g ., induction
vs. repression). Distribution of DE transcripts in these 17 clusters can
be found in Supplementary Tables S4-9, and the responses represented by
the other 29 clusters are described in Supplementary Figure S4.
Clusters comprising genes that display a similar drought response in the
presence or absence of Fld represent 31.5% of total DE transcripts, of
which 601 were induced (cluster 1) and 929 were repressed (cluster 2).
Cluster 1 was enriched in genes coding for components of the cytosolic
branch of glycolysis, ethylene synthesis, heat stress and signal
transduction associated to abscisic acid (Supplementary Figure S5;
Supplementary Table S4). Cluster 2 exhibited a remarkable
over-representation of genes belonging to cell wall metabolism such as
cellulose synthases, cellulases and pectinesterases, which declined in
both lines under water deficit (Supplementary Figure S5; Supplementary
Table S4). Several receptor kinases of the leucine-rich repeat family
were also repressed by drought irrespective of genotype.