Genetic dissection of ETHQV8.1, a QTL related with climacteric fruit ripening in melon.

Abstract

Fruit ripening is an essential process in crop plants, as it allows seed dispersion. Also, it has an economic importance due to its effect in fruit shelf-life and food waste. In flesh fruits there are two types of ripening: climacteric, with a characteristic peak of ethylene at the onset of ripening, coupled to an increase in cellular respiration; and non-climacteric, without ethylene peak production nor increase in respiration during the process. Tomato is considered the model fruit for climacteric ripening research, while strawberry is the model crop for non-climacteric ripening studies. Melon (Cucumis melo L.), apart from being an economically important crop worldwide, has the advantage of covering both climacteric and non-climacteric behaviors in the same species, making it a suitable candidate for genetic and genomic studies regarding fruit ripening._x000D_ To study this trait, we have developed two reciprocal introgression line (IL) populations with a high coverage of the donor genome, and segregating for ripening behavior, using as parental lines the climacteric ‘Védrantais’ (Ved) and the non-climacteric ‘Piel de Sapo’ (PS). In both IL populations, a previously reported QTL, ETHQV8.1, has been validated altering ripening behavior, as well as other QTLs controlling ripening and fruit morphology traits. Starting from the IL population with Ved genetic background, we have fine-mapped ETHQV8.1 to a 3.6 Kbp region containing a single annotated gene, ethylene responsive transcription factor 024 (CmERF024). Studying its expression in both IL populations and using the CRIPSR/Cas9 technique recently developed in melon, we reported CmERF024 as the causal gene of ETHQV8.1. When highly expressed, CmERF024 induced a climacteric response, milder when the gene was less or not expressed, apparently affecting chromatin structure and DNA accessibility._x000D_ To further investigate the role of ETHQV8.1, we have stacked this QTL with three previously reported QTLs affecting ripening in both Ved (MAK10.1) and PS (ETHQB3.5 and ETHQV6.3) genetic backgrounds. The epistatic interactions between these QTLs controled climacteric fruit ripening in melon, covering a broad spectrum of behaviors both in climacteric and non-climacteric genetic backgrounds. These results suggest that a small set of QTLs is sufficient to shape quantitative traits, proving powerful knowledge for applying in plant breeding._x000D_ Finally, to explore the relationships among ethylene production, respiration rate and primary metabolism, we have performed a metabolic profiling of Ved and PS, together with the ILs covering ETHQV8.1. The results showed that ETHQV8.1 is able to alter primary metabolism, ethylene production and cellular respiration, suggesting a crosstalk between the three processes. Also, some metabolites seemed especially relevant for the process, as citrate, and others may be interesting targets for melon plant breeding programs, as GABA._x000D_ As a summary, this PhD thesis has been focused on dissecting ETHQV8.1, a QTL related with climacteric ripening in melon. Combining molecular breeding with new breeding techniques we have validated the causal gene, CmERF024, which can delay significantly fruit ripening and potentially extend shelf-life. We have also analyzed its role in plant metabolism and its interactions with other known QTLs, providing a useful knowledge for melon breeding.

Date of Award	9 Jan 2023
Original language	English
Supervisor	Marta Pujol i Abajo (Director) & Jordi García Mas (Director)