1a.Objectives (from AD-416)
Characterize the expression patterns of ACS3 genes among elite apple cultivars, and elucidate the relationship of ACS3 expression and effectiveness of MCP treatment as well as subsequent postharvest fruit quality.
1b.Approach (from AD-416)
1. Fruit tissues representing different developmental stages will be collected for 12-16 cultivars, starting 30 days after full bloom till commercial maturity. 2. Apple fruits harvested at commercial maturity will be treated with1-MCP and fruit firmness changes of stored fruit will be assessed for at least 3 months. 3. Total RNAs will be isolated from above-mentioned fruit tissues using established procedure. 4. Gene-specific primers will be utilized to examine the expression patterns and dynamics on major ethylene biosynthesis enzyme encoding genes by quantitative real-time PCR methodology.
This project relates to objective 1 of the associated in-house project which seeks to identify factors that influence postharvest fruit quality and development of market limiting physiological disorders. Apple fruit ripening behaviors closely influence fruit quality such as fruit firmness and the postharvest firmness retention. Storability of apple fruit is ultimately associated with industry profitability and sustainability. Ethylene plays an important role in apple fruit development and its biosynthesis is catalyzed by two enzymes, i.e. ACS (1-aminocyclopropane-1-carboxylate synthase) and ACO (1-aminocyclopropane-1-carboxylic acid oxidase). The genetic form (or allele) of MdACS1 and MdACS3, are one of the genetic determinants of apple ripening and texture. Based on ACS3 expression analysis during 8-week on-tree maturation and ripening among 12 apple cultivars, cultivar-specific dynamics of MdACS3 expression acts as an “accelerator” of ripening and texture changes. Unlike MdACS1, the expression of MdACS3 is stimulated in the absence of ethylene action indicating a negative feedback regulation mechanism. Results from the second part of the project studying pre-harvest 1-MCP (Harvista™) application and postharvest 1-MCP treatments on expression of ethylene biosynthetic and receptor genes in ‘Golden Delicious’ apples are currently being summarized. Progress is monitored through annual submission of written reports to the funding organization.