Identification of genes possibly related to loss of quality in late-season 'Hass' avocados in Chile

The 'Hass' avocado (Persea americana Mill.) is the most important avocado variety cultivated worldwide. To reach destination markets, long-term cold storage and transit is usually needed to reduce fruit deterioration. However, low temperatures can affect fruit quality during ripening by increasing the incidence of several physiological disorders. In this work, 'Hass' avocados harvested in Chile in the early summer showed more incidence of physiological disorders than fruit harvested in the spring after storage for 40 d at 5 degrees C. As an initial approach to understand the types of metabolism affected during ripening after low temperature exposure, a forward suppression subtractive hybridization (SSH) cDNA library was constructed. A total of 117 differentially expressed genes encoding proteins involved in different biochemical pathways were identified. Genes related to stress response, protein synthesis and signal transduction were the most abundant. To corroborate our results with some of the previously found key differentially expressed genes, full length cDNA was obtained by rapid amplification of cDNA ends (RACE-PCR). Analysis of gene expression using real-time quantitative PCR was performed. Six avocado genes relating to cell wall, sugar and lipid metabolism were analyzed: polygalacturonase (PamPG), putative NAD(+)-dependent sorbitol dehydrogenase (PamSDH), stearoyl-ACP desaturase (SAD) and three putative acyl-CoA synthetase (PamACoAS1, 2, 3). The expression of all genes was up-regulated after ripening, especially in avocados harvested in the spring, except for PamSAD. These results imply that these genes could be related to the loss in quality observed in the fruit from the second harvest. Further studies should be performed to identify markers for quality loss in 'Hass' avocados. (c) 2012 Elsevier B.V. All rights reserved.