3.7 Genes whose drought response was ameliorated by chloroplast
Fld
A significant number of genes showed different expression patterns under
water stress conditions depending on the presence of Fld, exhibiting
lower induction (clusters 5 and 6) or repression (clusters 7 and 8) inStpfld 252 leaves relative to WT counterparts (Figure 5,
Supplementary Table S6). These four clusters comprise 33% of total DE
transcripts (1611 genes), and collectively represent the most common
response to treatment and genotype. Cluster 5 contained 546 genes whose
drought-dependent induction was completely abolished by Fld, while for
274 genes of cluster 6 the effect of Fld was only partial.
Cluster 5 contained genes involved in sucrose metabolism, including
several sucrose synthase isoforms (Figure 5, Supplementary Table S6). It
also harbored genes involved in the regulation of isoprenoid metabolism.
Isoprenoids are a large and diverse group of molecules that include
photosynthetic pigments (chlorophylls and carotenoids), components of
different electron transport chains (plastoquinone, ubiquinone),
hormones (abscisic acid, gibberellins, cytokinins and brassinosteroids),
membrane-associated phytosterols and antimicrobials (phytoalexins).
Cluster 6 was enriched in pathways related to abiotic stress responses,
including various heat-responsive transcription factors and heat-shock
proteins (Figure 5, Supplementary Table S6). Most members of this
category function as chaperones involved in protein folding, assembly
and translocation.
Clusters 7 and 8 exhibit a remarkable over-representation of genes
associated to photosynthesis, including components of the
light-harvesting complexes, the photosynthetic electron transport chain
(PETC) and the Calvin-Benson cycle (Figure 5, Supplementary Table S6).
In addition, cluster 7 (528 genes) includes transcripts encoding
glycolytic enzymes (e.g. , phosphoglycerate kinase) and enzymes
involved in homoserine and γ-aminobutyrate (GABA) synthesis. Cluster 8
(263 genes), in turn, contained transcripts related to cell wall
metabolism, although most of the genes belonging to this functional
category were grouped in cluster 2.
A small number of genes showed drought responsiveness only inpfld 252 plants (Figure 6a, Supplementary Table S7). Cluster 9
contained 111 induced genes, with over-representation of transcripts
associated to isoprenoid metabolism, whereas cluster 10 included 117
drought-repressed genes, and was enriched in transcripts related to the
auxin and minor carbohydrate categories, particularly raffinose
synthesis (Figure 6a, Supplementary Table S7).