454 Sequencing for the Identification of Genes Differentially Expressed in Avocado Fruit (cv. Fuerte) Infected by Colletotrichum gloeosporioides

The anthracnose pathogen, Colletotrichum gloeosporioides (Penz.) Penz. & Sacc., is a major cause of disease in the avocado industry, causing significant economic losses, and infects all cultivars. In South Africa, cvs Fuerte and Hass are the most widely grown. Identification of genes differentially expressed in avocado during infection with the fungus represents an important step towards understanding the plants defence responses and would assist in designing appropriate intervention strategies. In this study, 454 sequencing and analysis of the transcriptome of infected cv. Fuerte avocado fruits were performed using the Roche 454 GS FLX Titanium platform. cDNA libraries enriched for differentially expressed genes were constructed from unharvested and harvested avocado fruit tissues collected after 1, 4 and 24h postinfection (early response) and after 3, 4, 5 and 7days postinfection (late response), then sequenced. RT-PCR was used to validate the sequencing results. The single sequencing run produced 215781 reads from the transcriptome with an average sequence length of 252-300 nucleotides. A total of 70.6megabases of sequence data were generated and subjected to BLAST searches from which 639 genes encoding proteins functioning in metabolism, signal transduction, transcriptional control, defence, stress, transportation processes and some genes with unknown functions were identified. Avocado is able to respond to C. gloeosporioides infection by exhibiting a sophisticated molecular system for pathogen recognition and by activating structural and biochemical defence mechanisms. This study represents the first transcriptome analysis of avocado fruit following infection with C. gloeosporioides, and the findings are discussed in relation to the known or putative functions of the gene products.