3.9 Drought-responsive genes primed by Fld expression
Clusters 14-17 included DE transcripts that responded to water limitation but were also modulated by Fld in the same direction under normal growth conditions (Figure 6c, Supplementary Table S9). Cluster 14 contained 76 transcripts that were induced by chloroplast Fld to the levels attained in drought-stressed WT plants, while genes grouped in cluster 15 (35 members) were further up-regulated by water limitation in both WT and Stpfld 252 plants. DE genes over-represented in these clusters belonged to the ethylene and minor carbohydrate functional categories, including a myo-inositol-1-phosphate synthase (MIPS) that catalyzes the first step of myo-inositol biosynthesis.
Cluster 16 comprised 127 genes whose expression was repressed by Fld under growth chamber conditions to the levels attained by the drought treatment in both lines (Figure 6c, Supplementary Table S9). Most conspicuous among them was the ethylene responsive factor 5 (ERF5). Finally, cluster 17 included 52 transcripts that were repressed by chloroplast-targeted Fld in the absence of stress, and further by drought in both lines (Figure 6c, Supplementary Table S9), with no specifically enriched functional category.