Identified three genes involved in melon ripeningNew research would allow the development of melon varieties with a longer shelf life, thus helping reduce food waste
A study by CRAG and the Institute of Agrifood Research and Technology (IRTA), with the participation of the Institute of Biology of the École Normale Supérieure (IBENS) in Paris, has identified the role of three genes in melon ripening. The finding sheds light on the mechanism of ripening of this fruit, “a complex process involving several genes that need to be identified in order to understand how it works”, says Marta Pujol, IRTA researcher at CRAG involved in the research. Knowing this process is key to developing new varieties of melon with longer ripening tempos, “a highly demanded request both by the market and by seed companies because it would extend melon’s shelf life and, consequently, reduce food waste”, Pujol adds. The results of the study, which provide the foundation to understand the ripening process of melons, have been published in the journals Frontiers in Plant Science and Journal of Experimental Botany, the latter selected as the editor’s choice article of the issue for its substantial contribution to the field.
Cantaloupe is a climacteric variety of melon. This means that, like fruits such as tomatoes, it continues to ripen once it has been harvested, and it does so by emitting ethylene, a plant hormone that induces climacteric-type ripening. Thus, once harvested, climacteric fruits tend to have a shorter life than others. However, fruits that are not climacteric, such as grapes, oranges or melons of the “Toad Skin” (piel de sapo) variety, do not ripen using ethylene, but do so through other mechanisms that are not yet sufficiently known; this means that, in many cases, their organoleptic traits remain stable for longer than in climacteric fruits. One of the current challenges of plant genomics is to find out the mechanisms involved in fruit ripening. Historically, the tomato has been used as a model plant to understand this process, and the research carried out thus far “has allowed us to advance our knowledge of the mechanisms that regulate climacteric ripening”, explains Jordi Garcia-Mas, IRTA researcher at CRAG and also one of the authors of the study. Garcia-Mas co-led the research that enabled the sequencing of the melon genome in 2012.
In the IRTA, CRAG and IBENS study, the CRISPR/Cas9 gene editing technique has been implemented for the first time to edit melon genes of agronomic interest. Three genes involved in the climacteric ripening of melon were identified ―CmCTR1, CmROS1 and CmNAC-NOR―, and researchers caused mutations in such genes using this novel technique to find out their role. “We saw that the inhibition of the expression of the first two genes led to an accelerated maturation of the fruit”, says Andrea Giordano, CRAG researcher and first author of one of the works. “In the case of CmNAC-NOR”, adds Pujol, “we observed that one mutation, nor-3, managed to delay ripening by eight days, while another mutation, nor-1, completely blocked it”.
Which of these mutations is best for new melon varieties with a longer shelf life? Marta Pujol is cautious when replying: “At the moment, we know the function of the gene, not which will be better or which will be worse; the next step is to evaluate the quality of the resulting melons”. As Pujol claims, “it can be very interesting to delay ripening, as long as the melons do not lose other characteristics such as aroma, sugar or carotene content, which give organoleptic and nutritional quality to the fruit”. For Garcia-Mas, one of the most interesting points of the findings is that it can be a first step to “turn a climacteric melon into a less climacteric one and, consequently, preserve it for a longer time”.
In any case, the research led by Jordi Garcia-Mas’s group at CRAG over the years has shown the usefulness of the melon as an alternative model to the tomato to study both climacteric and non-climacteric ripening.
From the laboratory to the market
“Thanks to our research, we now know what genes we should look at to extend the life of melon, but, for now, using the mutants obtained by CRISPR/Cas9 editing is not possible because in Europe they are considered as genetically modified organisms (GMOs)”, notes Garcia-Mas. Nevertheless, regulations in other countries, such as Brazil, Japan or the USA, do allow it. “Now that we know some of the genes involved in melon ripening, the only choice in Europe is to find natural variants of these genes that prolong shelf life and to use them in conventional genetic breeding programmes, an option that is of great interest to seed companies”.
Articles of reference
Andrea Giordano, Miguel Santo Domingo, Leandro Quadrana, Marta Pujol, Ana Montserrat Martín-Hernández, Jordi Garcia-Mas. CRISPR/Cas9 gene editing uncovers the roles of CONSTITUTIVE TRIPLE RESPONSE 1 and REPRESSOR OF SILENCING 1 in melon fruit ripening and epigenetic regulation, Journal of Experimental Botany. 2022 Jun 24;73(12):4022-4033. https://doi.org/10.1093/jxb/erac148
Bin Liu, Miguel Santo Domingo, Carlos Mayobre, Ana Montserrat Martín-Hernández, Marta Pujol, and Jordi Garcia-Mas. Knock-Out Of Cmnac-NOR Affects Melon Climacteric Fruit Ripening. Frontiers In Plant Science. 2022 Jun 10;13:878037. https://doi.org/10.3389/fpls.2022.878037
About the authors and the funding of the study
This work was supported by grants AGL2015–64625-C2–1-R and RTI2018-097665-B-C2 funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe,” the Severo Ochoa Programme for Centres of Excellence in R&D 2016–2010 (SEV-2015-0533) funded by MCIN/AEI/10.13039/501100011033, the CERCA Programme/Generalitat de Catalunya and 2017 SGR 1319 grant from the Generalitat de Catalunya to Jordi Garcia-Mas. Bin Liu was also supported by grants from Youth Project of National Natural Science Foundation of China (31902035), The International Postdoctoral Exchange Fellowship Program of China (20170053), and a postdoctoral grant from the Severo Ochoa Programme for Centres of Excellence in R&D 2016–2010 (SEV-2015-0533). Carlos Mayobre was supported by FI grant from the Secretaria d’Universitats i Recerca del Departament d’Empresa i Coneixement de la Generalitat de Catalunya and the co-funding of the European Social Fund (ESF)—“ESF is investing in your future”. Andrea Giordano was supported by the European Union’s Horizon 2020 research and innovation programme under Marie Skłodowska-Curie (grant agreement No. 793090). Miguel Santo Domingo was supported by a FPI grant from the Spanish Ministry of Economy and Competitiveness BES-2017-079956 funded by MCIN/AEI/ 10.13039/501100011033 and by ‘ESF Investing in your future’. Work in the Quadrana group is supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement no. 948674).