3.2 Microarray analysis of drought-stressed plants expressing chloroplast Fld
Transcriptional profiling is a powerful experimental approach to investigate plant responses to environmental challenges. Most transcriptome analyses on water-restricted potatoes have been performed on plants showing stress symptoms (Evers et al. 2010; Kondrák, Marincs, Antal, Juhász & Bánfalvi 2012; Zhang et al. 2014). Fld provided protection against drought effects occurring at a pre-symptomatic stage that might contribute to the differential tolerance exhibited by Fld-expressing plants. Therefore, a genome-wide transcriptional profiling was carried out using WT and Stpfld 252 leaves sampled at 3 days of treatment as RNA source, together with their corresponding watered controls. Once again, the Stpfld 252 line was chosen because of its high levels of Fld accumulation and drought protection.
Gene expression profiles were determined using a single-channel Agilent potato microarray consisting of 42034 probes. We did not carry out any filtering for potential redundant probes mapping the same transcript due to the difficulties related to the highly heterozygous nature of potato genomes, their polyploidy variance, the different accessions used the microarray design, the reference genome sequencing and our current work. Functional annotation was based on the Mapman ontology using the GoMapman website resource (Ramšak et al. 2014). More than 80% of the genes included in the microarray could be assigned to a functional category. The total number of leaf-expressed genes that passed the background correction and filtering processes (Materials and Methods) was similar for the two genotypes under control conditions and represented about 75% of the total genes present in the microarray.