Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2011
Publication Date: 5/26/2011
Citation: Varanasi, V., Mattheis, J.P., Rudell Jr, D.R., Zhu, Y., Shin, S.B. 2011. Expression profiles of MdACS3 gene suggest function as an accelerator of apple (Malus x domestica) fruit ripening. Postharvest Biology and Technology. 62:141-148. Interpretive Summary: While ethylene’s role promoting pome fruit ripening is indisputable, most previous studies were focused on ethylene biosynthesis during climacteric ripening. Little information is available regarding a pre-climacteric ethylene biosynthesis gene MdACS3, which contributes to ethylene biosynthesis in apple fruit tissues before climacteric ripening. To understand the role of this gene on apple fruit ripening and quality, cultivar-specific activities of the MdACS3 gene were studied among 14 apple cultivars in the early stage of fruit maturation and ripening. The results suggest activities of MdACS3 are generally correlated with apple fruit ripening season, i.e. stronger MdACS3 expression primarily results in early fruit ripening, most likely due to early activation of MdACS1. Stronger activity of MdACS3 is also associated with less firm fruit. The relationship between the activity of MdACS3 gene and 1-MCP treatment efficacy is less clear, indicating other factors are involved. Results from this study are essential in developing tools for apple breeding and fruit quality management.
Technical Abstract: Ethylene plays an important role in diverse physiological and developmental processes of plants. Ethylene is synthesized by a short pathway and catalyzed by two enzymes, i.e. ACS and ACO. In apple fruit tissues, at least two ACS genes, MdACS1 and MdACS3, are expressed. While MdACS1 expresses only at late ripening stages, expression of MdACS3 can be detected as early as 6 weeks before physiological maturity. The objective of this study was to characterize MdACS3 expression in relation to cultivar-specific apple fruit ripening and quality by quantitative RT-PCR. Among 14 apple cultivars investigated, two distinguishable expression patterns of MdACS3 gene were observed. Pattern 1 showed steadily-increasing with high level expression, and pattern 2 exhibited low level expression with a transient peak. These two expression patterns appear to correlate with fruit ripening season and fruit firmness at physiological maturity. For example, ‘Sunrise’ with highest levels of MdACS3 expression had the earliest ripening season and lowest firmness values; while ‘Pink Lady’ with very low levels of MdACS3 expression showed the highest firmness and with late ripening season. Unlike MdACS1, the expression of MdACS3 is not inhibited by 1-MCP treatment, rather a slight increase in expression level was observed after 1-MCP treatment. The relationship between MdACS3 expression patterns and the timing of MdACS1 activation and post-harvest fruit storability are discussed.