Identification and characterization of two putative genes encoding acetyl-coenzyme A carboxylase subunits that are possibly associated with internal browning during cold storage of ‘Hass’ avocados (Persea americana Mill.)

Abstract

Cold storage is widely used to extend the postharvest life of ‘Hass’ avocados (Persea americana Mill.). However, prolonged low-temperature storage results in the development of chilling-induced physiological disorders. Additionally, the response of avocados to cold storage depends on their stage of maturity, as late-harvest avocados are more susceptible to developing physiological disorders than those that are harvested early in the season. To understand the molecular mechanisms that cause physiological disorders in cold-stored ‘Hass’ avocados, we sought to identify and characterize the lipid metabolism-related genes. In this work, we focused our analysis on the genes that encode a multi-subunit acetyl-CoA carboxylase enzyme (MS-ACCase), which is one of the key enzymes in fatty acid biosynthesis. Two avocado MS-ACCase subunits were identified by in silico analysis, a biotin carboxylase (BC) and a biotin carboxyl carrier protein (BCCP). Transcriptional qPCR analyses of both identified gene subunits were performed in avocados that had been harvested both early and late in the season after 40d of storage at 0 and 5°C and subsequent ripening at 20°C. For both harvest dates, PamACCase-BC and PamACCase-BCCP transcripts increased in ripe fruit after cold storage at 5°C; this increase was significant for PamACCase-BCCP. A similar expression pattern was observed in ripe avocados from early-harvested fruit after cold storage at 0°C; however, significant down-regulation of PamACCase-BC and PamACCase-BCCP expression was observed in ripe late-harvested avocados, suggesting that these fruit have senesced. A control study involving late-harvested avocados demonstrated that the expression of these genes did not change throughout ripening. Thus we suggest that the MS-ACCase BCCP subunit might be transcriptionally regulated during physiological disorder development in cold-stored ‘Hass’ avocados.