Understanding Kiwi Fruit Ripening Through Genetic Variations

Jim Crocker
18th May, 2024

Understanding Kiwi Fruit Ripening Through Genetic Variations

The seven representative Actinidia chinensis varieties selected for this study show consistent grouping based on their genetic relatedness (a), fruit flesh color (b), and secondary metabolite profiles (c).

Image adapted from: Wang et al. / CC BY (Source)

Key Findings

  • Researchers at Anhui Agricultural University studied the genetic basis of chlorophyll retention in green-fleshed kiwifruit
  • They identified a structural variation in the AcBCM gene promoter that leads to high expression of AcBCM during late fruit development
  • This high expression of AcBCM regulates the enzyme AcSGR2, causing chlorophyll accumulation and preventing the usual degreening seen in other fruits
Fruit ripening is a critical phase in the life cycle of many plants, transforming fruit from an unripe state that deters consumption to a ripe state that attracts seed-dispersing animals. This process involves significant biochemical changes, including the loss of chlorophyll, known as degreening. Interestingly, kiwifruit is one of the few fruits that may maintain its green flesh even after ripening, thanks to the retention of chlorophyll. A recent study conducted by researchers at Anhui Agricultural University provides new insights into the genetic variations that contribute to this unique characteristic[1]. The study constructed a graph-based pangenome by analyzing 14 chromosome-scale haplotype-resolved genome assemblies from seven representative cultivars or lines of Actinidia chinensis, the species to which kiwifruit belongs. This comprehensive pangenome revealed a total of 49,770 non-redundant gene families, with 46.6% being core genes and 53.4% being dispensable genes. Additionally, the study identified 84,591 non-redundant structural variations (SVs), which are significant rearrangements in the genome that can affect gene function and regulation. One of the key findings of the study is the identification of an SV in the promoter region of the AcBCM gene. This SV is responsible for the high expression of AcBCM during the late developmental stages of the fruit, which in turn causes chlorophyll accumulation in green-fleshed kiwifruit by post-translationally regulating AcSGR2, a key enzyme involved in chlorophyll catabolism. This discovery sheds light on the genetic basis of chlorophyll retention in kiwifruit and provides valuable information for further research on genome evolution, domestication, and genomics-assisted breeding. Previous studies have highlighted the importance of chlorophyll in plant tissues. Chlorophylls are crucial for photosynthesis and are found abundantly in green fruits and vegetables. These pigments and their derivatives possess therapeutic properties, including antioxidant, antimutagenic, and anti-cancer activities[2]. However, chlorophyll is usually degraded during the ripening process in most fruits. For example, in gold-fleshed kiwifruit (Actinidia chinensis), chlorophyll is degraded to colorless catabolites upon ripening, leaving yellow carotenoids visible[3]. The new study builds on these findings by identifying specific genetic variations that regulate chlorophyll degradation in kiwifruit. The research methods employed in this study involved constructing a high-quality pangenome that integrates both reference genome sequences and variant information. This approach facilitated the identification of structural variations related to fruit color. By focusing on the SV in the promoter of the AcBCM gene, the researchers could pinpoint its role in the high expression of AcBCM during the late developmental stages of the fruit. This, in turn, leads to the accumulation of chlorophyll in green-fleshed kiwifruit by regulating the activity of AcSGR2. The findings of this study have significant implications for plant biology and food security. Understanding the genetic basis of chlorophyll retention in kiwifruit can help in developing new cultivars with desirable traits, such as extended shelf life and enhanced nutritional value. Moreover, the identification of key genetic variations can aid in genomics-assisted breeding, allowing for the selection of traits that improve fruit quality and resistance to decay. In conclusion, the recent study by Anhui Agricultural University provides valuable insights into the genetic variations that regulate chlorophyll retention in kiwifruit. By constructing a high-quality pangenome and identifying a novel structural variation in the AcBCM gene, the researchers have unraveled the genetic basis of this unique trait. These findings build on previous research and open new avenues for further investigation into genome evolution, domestication, and the development of improved fruit cultivars.

FruitsGeneticsPlant Science

References

Main Study

1) Graph-Based Pangenome of Actinidia chinensis Reveals Structural Variations Mediating Fruit Degreening.

Published 17th May, 2024

https://doi.org/10.1002/advs.202400322

Related Studies

2) Enhancing Health Benefits through Chlorophylls and Chlorophyll-Rich Agro-Food: A Comprehensive Review.

https://doi.org/10.3390/molecules28145344

3) The control of chlorophyll levels in maturing kiwifruit.

https://doi.org/10.1007/s00425-012-1723-x


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