RNA-Seq reveals different responses to drought in Neotropical trees from savannas and seasonally dry forests.

BACKGROUND: Water is one of the main limiting factors for plant growth and crop productivity. Plants constantly monitor water availability and can rapidly adjust their metabolism by altering gene expression. This leads to phenotypic plasticity, which aids rapid adaptation to climate changes. Here, we address phenotypic plasticity under drought stress by analyzing differentially expressed genes (DEG) in four phylogenetically related neotropical Bignoniaceae tree species: two from savanna, Handroanthus ochraceus and Tabebuia aurea, and two from seasonally dry tropical forests (SDTF), Handroanthus impetiginosus and Handroanthus serratifolius. To the best of our knowledge, this is the first report of an RNA-Seq study comparing tree species from seasonally dry tropical forest and savanna ecosystems. RESULTS: Using a completely randomized block design with 4 species × 2 treatments (drought and wet) × 3 blocks (24 plants) and an RNA-seq approach, we detected a higher number of DEGs between treatments for the SDTF species H. serratifolius (3153 up-regulated and 2821 down-regulated under drought) and H. impetiginosus (332 and 207), than for the savanna species. H. ochraceus showed the lowest number of DEGs, with only five up and nine down-regulated genes, while T. aurea exhibited 242 up- and 96 down-regulated genes. The number of shared DEGs among species was not related to habitat of origin or phylogenetic relationship, since both T. aurea and H impetiginosus shared a similar number of DEGs with H. serratifolius. All four species shared a low number of enriched gene ontology (GO) terms and, in general, exhibited different mechanisms of response to water deficit. We also found 175 down-regulated and 255 up-regulated transcription factors from several families, indicating the importance of these master regulators in drought response. CONCLUSION: Our findings show that phylogenetically related species may respond differently at gene expression level to drought stress. Savanna species seem to be less responsive to drought at the transcriptional level, likely due to morphological and anatomical adaptations to seasonal drought. The species with the largest geographic range and widest edaphic-climatic niche, H. serratifolius, was the most responsive, exhibiting the highest number of DEG and up- and down-regulated transcription factors (TF).

Isolation and characterization of microsatellite loci in Cabralea canjerana (Meliaceae).

PREMISE OF THE STUDY: Microsatellite primers were developed in the native Neotropical tree species Cabralea canjerana (Vell.) Mart. (Meliaceae) to study population genetics in some Atlantic Forest fragments of Brazil. This species is suitable for use in reforestation and is commercially important due to its high-quality wood. METHODS AND RESULTS: In this study, eight microsatellite loci were isolated from an enriched C. canjerana genomic library. These are the first microsatellite loci described for this genus. Genetic diversity analyses were carried out using 30 individuals and six polymorphic loci. An average of 11.2 alleles was found, and the observed heterozygosity was 0.65. CONCLUSIONS: The microsatellite markers described here are valuable tools for further population genetic studies of the species.