Functional analysis of the banana genome by gene tagging and sage

Abstract

Banana is a good candidate for functional genomics because it has a relatively small genome size (600 Mbp) and important characteristics such as climacteric fruit, parthenocarpy or vegetative propagation, which are absent in model organisms. For the functional analysis of the banana genome we have adopted two approaches: genome tagging and expression profiling by SAGE. First, a platform has been developed to generate large transgenic populations for the isolation of constitutive and inducible promoters via activation of the luciferase reporter gene. Out of 20,000 transgenic cell colonies screened, 2.5% expressed a modified luciferase tag, and 30 transgenic lines showed constitutive expression with a higher or comparable activity to the 35S promoter-driven control. As an example, tagging and molecular characterization of a metallothionein gene and a novel unknown gene will be presented. Further, SuperSAGE libraries with more than 5,000 unique 26-bp long tags were generated from banana leaves, which allowed a quantitative analysis of the transcriptome. Besides the identification of extremely low-abundance transcripts putative differentially expressed genes were identified after infection with Mycosphaerella fijiensis, the most important fungal pathogen of banana. Extension of both types of tags to full-length genes is in progress and the functional analysis of these genes will contribute to the understanding of the banana genome.