The Transcriptome of Savanna Species are Less Responsive to Drought Compared to Forest Species of the Neotropical Tabebuia Alliance

Drought is arguably the worst challenge facing agriculture. In plants, drought tolerance is a highly complex trait. Studies have pointed to a widespread change in the transcriptome of cultivated plants submitted to water deficit. However, no study has been conducted on plant species that evolved in stressful environments, such as savannas. Species of ipes (Tabebuia Alliance) have a wide neotropical distribution, occupying areas with different soil and climatic conditions. We studied the effect of drought on the transcriptome of four ipe species, two from the Brazilian savanna (Tabebuia aurea and Handroanthus ochraceus) and two from forest environments (Handroanthus impetiginosus and Handroanthus serratifolius). The 4 × 2 (species × water treatments) experiment had three biological replicates. Plants grew for 10 months in three liter pots, when irrigation was withheld from drought treated plants until substrate reached ~20% field capacity. Xylem tissue was collected for RNA extraction and sequencing (2x100bp PE) on a HiSeq 2000 platform. Sequences were aligned in the H. impetiginosus reference genome and differentially expressed genes (DEG) were identified with DESeq2/R package. Our results indicate that stress adapted plants, such as those from the Brazilian savanna, are less responsive to drought. While forest species H. impetiginosus and H. serratifolius had 4,844 and 947 DEG, savanna species T. aurea and H. ochraceus had only 277 and 8 DEG. Gene Ontology enrichment analyses indicate that, while forest species have a wide up-regulation of stress responsive genes, savanna species exhibits up-regulation of sugar metabolism genes, possibly for osmotic adjustment.