De novo assembly of Vriesea carinata leaf transcriptome to identify candidate cysteine-proteases

Vriesea carinata is an endemic bromeliad from the Brazilian Atlantic Forest. It has trichome and tank system in their leaves which allows to absorb water and nutrients. It belongs to Bromeliaceae family, which includes several species highly enriched of cysteine-proteases (CysPs). These proteolytic enzymes regulate processes as senescence, cell differentiation, pathogen-linked programmed cell death and mobilization of proteins. Although, their biological importance, there are not genomic resources in V. carinata that can help to identify and understand their molecular mechanisms involved in different biological processes. Thus high-throughput transcriptome sequencing of V. carinata is necessary to generate sequences for the purpose of gene discovery and functional genomic studies. In the present study, we sequenced and assembled the V. carinata transcriptome to the identification of CysPs. A total of 43,232 contigs were assembled for the leaf tissue. BLAST analysis indicated that 23,803 contigs exhibited similarity to non-redundant Viridiplantae proteins. 28.24% of the contigs were classified into the COG database, and gene ontology categorized them into 61 functional groups. A metabolic pathway analysis with KEGG revealed 9679 contigs assigned to 31 metabolic pathways. Among 16 full-length CysPs identified, 11 were evaluated in respect to their expression patterns in the leaf apex, base and inflorescence tissues. The results showed differential expression levels of legumain, metacaspase, pyroglutamyl and papain-like CysPs depending of the leaf region. These results provide a global overview of V. carinata gene functions and expression activities of CysPs in those tissues.