Low frequency of the wild-type freezing-tolerance LsCBF7 allele among lettuce population suggest negative selection during domestication and breeding

Authors: Park, Sunchung - Sun; SHI, AINONG - University Of Arkansas; Mou, Beiquan

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2024
Publication Date: 5/18/2024
Citation: Park, S., Shi, A., Mou, B. 2024. Low frequency of the wild-type freezing-tolerance LsCBF7 allele among lettuce population suggest negative selection during domestication and breeding. Theoretical and Applied Genetics. 137:135. https://doi.org/10.1007/s00122-024-04643-8.
DOI: https://doi.org/10.1007/s00122-024-04643-8

Interpretive Summary: Lettuce is a widely popular vegetable, and for year-round production, its cultivation continues through the colder months in regions with milder winters. However, these areas often experience freezing temperatures, leading to substantial yield losses, making it essential to develop lettuce varieties that can withstand the cold. In our research, we focused on understanding how lettuce can become more resilient to freezing temperatures. We discovered a specific gene, LsCBF7, in lettuce that plays a crucial role in this process. We investigated its role and found that it contributes to improved freezing tolerance in certain lettuce varieties, particularly those from colder regions. This discovery opens the possibility of breeding lettuce varieties that can thrive in colder climates. However, we also found that this gene might be linked to a less desirable trait called early bolting. To fully harness the potential of this gene for freezing tolerance, we need to find a way to separate it from the early bolting trait. This research could lead to lettuce varieties that are more resilient to freezing temperatures, ensuring a consistent supply of this nutritious vegetable, even during colder months.

Technical Abstract: Lettuce is one of the most consumed vegetables globally. Typically grown in temperatures ranging from 13 to 21°C, its cultivation continues through the colder months in regions with milder winters. However, these areas often experience freezing temperatures, leading to substantial yield losses. Therefore, the development of freezing-tolerant lettuce varieties has become a long-term goal of lettuce breeding programs. Despite its significance, our understanding of freezing tolerance in lettuce remains limited. Plants evolve a coping mechanism against freezing, known as cold acclimation, whereby they can increase freezing tolerance when pre-exposed to low nonfreezing temperatures. The CBF pathway is well-known for its central role in cold acclimation. Previously, we identified 14 CBF genes in lettuce and discovered that one of them, LsCBF7, had a loss-of-function mutation. In this study, we uncovered that accessions from colder regions carried the wild-type allele of LsCBF7 and this allele contributed to increased freezing tolerance, with 14% of the lettuce population carrying this allele. Interestingly, in wild lettuce (L. serriola) that is considered a progenitor of cultivated lettuce, this wild-type allele was much more common, with a frequency of 90%. This finding suggests that this wild-type allele may have undergone negative selection during the domestication or breeding of lettuce. Our data strongly indicate that this allele could be linked to early bolting, an undesirable trait in lettuce, which may have driven the negative selection. While this wild-type allele shows promise for improving freezing tolerance in lettuce, it is crucial to decouple it from the early bolting trait to fully harness its potential in lettuce breeding.