3.3 Chloroplast Fld affected gene expression patterns of potato leaves in the absence of stress
We first evaluated the effect of chloroplast Fld on gene expression in leaves of potato plants grown under normal conditions. Analysis of transcript levels in WT and Stpfld 252 leaves showed that 1097 genes were induced 2-fold or more by Fld relative to WT siblings, with 181 increasing more than 4-fold in their expression. Also, 578 transcripts declined to 50% or less in Stpfld 252 leaves compared to the wild type, 54 of which accumulated below or equal to 25% (Figure 3, Supplementary Table S2). Functional enrichment analysis of these DE transcripts showed that among the genes induced in Stpfld 252 plants there was a remarkable over-representation of those associated to protein degradation by the proteasome (Figure 3, Supplementary Table S2). It is worth noting that a similar induction pattern has been observed in Fld-expressing tobacco plants (Pierella Karlusich et al. 2017), indicating that plastid-located Fld exerts a key regulatory role in the accumulation of proteasomal components in different species, presumably through modulation of chloroplast redox chemistry.
Functional categories that displayed differential repression by Fld comprised trehalose synthesis, nitrate metabolism, amino acid degradation and traits associated to metal uptake and utilization such as Cd- and Al-induced proteins, Cu chaperones and Fe-chelate reductases. Noteworthy, ethylene metabolism and signaling were consistently down-regulated in Stpfld 252 plants, including 29 genes encoding transcription factors of the apetala2/ethylene-responsive family (Figure 3, Supplementary Table S2). These observations also agree with earlier reports on Fld-expressing tobacco plants (Pierella Karlusich et al. 2017). The mechanisms underlying this repression are unknown and deserve further investigation.