Abstract
The physiology of fruit ripening is defined as either ‘climacteric’ or ‘non-climacteric’. In climacteric fruit respiration during ripening increases until it reaches a peak, which is accompanied by an increase in autocatalytic ethylene production, whereas the respiration of non-climacteric fruit does not increase and they have no requirement for ethylene to complete their ripening. In an attempt to gain further insight into the involvement of autocatalytic ethylene production with the climacteric rise in respiration, tomato fruit were harvested at three defined stages of maturity prior to the climacteric peak (mature green, breaker, and early orange) and immediately exposed to the gaseous molecule 1-methylcyclopropene (1-MCP). The gene expression profile at each of these stages was monitored after 24 h, using an Affymetrix tomato microarray chip. This approach enabled us to identify ethylene responsive genes that are commonly regulated at early stages of ripening, as well as new candidate genes. In addition, 1-MCP treatment affected the levels of metabolites related to methionine biosynthesis. Methionine feeds climacteric ethylene production and we found that promotors of the genes of enzymes that catalyze the production of homoserine and homocysteine (aspartokinase/homoserine dehydrogenases and cystathionine beta lyase, respectively), precursors in the methionine pathway, contain the AtSR1 binding motif. This binding motif is recognized by ethylene activated transcription factors, hence indicating a role for ethylene in methionine synthesis during early ripening, explaining the autocatalytic ethylene production during subsequent ripening stages.
Highlights
The physiology of fruit ripening is defined as either ‘climacteric’ or ‘non-climacteric’
Fruit at mature green (MG), breaker (BR), and early orange (EO) stages were harvested in the early morning hours and immediately transferred to the laboratory
We aimed to deepen our understanding of ethylene regulated gene expression at the early stages of the ripening process and the beginning of the climacteric ethylene burst
Summary
The physiology of fruit ripening is defined as either ‘climacteric’ or ‘non-climacteric’. Respiration reaches a peak, which is accompanied by an autocatalytic increase in ethylene production, whereas the respiration of non-climacteric fruit does not increase and only minimal quantities of ethylene are commonly produced [1,2]. Agronomy 2020, 10, 1669 of the rise in respiration, which accompanies fruit ripening, while non-climacteric fruit at any stage of maturity respond with a transient increase in respiration, often without any obvious change in ripening, apart from chlorophyll degradation, as observed in citrus fruit [3]. Climacteric fruit are commercially harvested at completion of their growth and ethylene plays a major role in the ripening process during subsequent storage and marketing. The ethylene biosynthetic pathway is well understood; there is still a lot to be disclosed and understood regarding its role and regulation during climacteric ripening
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