Anthocyanins Double the Shelf Life of Tomatoes by Delaying Overripening and Reducing Susceptibility to Gray Mold
Yang Zhang, Eugenio Butelli, Rosalba De Stefano, Henk-jan Schoonbeek, Andreas Magusin, Chiara Pagliarani, Nikolaus Wellner, Lionel Hill, Diego Orzaez, Antonio Granell, Jonathan D.G. Jones, Cathie Martin
In case you have not read my article ‘The cool colour’, anthocyanins are compounds in plants that protect them from environmental stress and might also protect them against diseases. I know that it might be difficult to have access to scientific articles if you are not a student (the majority is behind a paywall), so I have included the abstract below with the important take-home messages highlighted.
Abstract
Shelf life is an important quality trait for many fruit, including tomatoes. We report that enrichment of anthocyanin, a natural pigment, in tomatoes can significantly extend shelf life. Processes late in ripening are suppressed by anthocyanin accumulation, and susceptibility to Botrytis cinerea, one of the most important postharvest pathogens, is reduced in purple tomato fruit. We show that reduced susceptibility to B. cinerea is dependent specifically on the accumulation of anthocyanins, which alter the spreading of the ROS burst during infection. The increased antioxidant capacity of purple fruit likely slows the processes of overripening. Enhancing the levels of natural antioxidants in tomato provides a novel strategy for extending shelf life by genetic engineering or conventional breeding.
Tomato with Botrytis cinera (fungus). Image from World Tomato Society.
Explanation of the article
We all want food to last longer, right? Shelf life is incredibly important, and even though there is technology nowadays helping to decrease food waste in our fridges and supermarkets, it is not enough. One of the strategies that is addressed in this article is genetically engineer fruit to last longer, in this case, tomato.
This team genetically engineered tomatoes to have more anthocyanins. This family of compounds helps plants survive environmental stress (such as pH and temperature, basically, it works as an immune system to the plant). They found out that tomatoes with more anthocyanins will last longer, improving their shelf life. Not just that, but they also found that the enhancement of anthocyanins levels also improved the plant’s susceptibility to the pathogen Botrytis cinera (grey mould).
But why did the tomatoes last longer?
As said above, the concentration of anthocyanins increased, which improved the accumulation of these compounds in the cells. This altered the spreading of reactive oxygen species (ROS) burst during infection by the pathogen. The increase of antioxidants in cells or reduction of ROS can lead to the extension of shelf life. In case you do not know, antioxidants can damage cells and their DNA, so organisms generally develop mechanisms to neutralise these free radicals; plants developed anthocyanins for this. That is why it is important to eat plants with high antioxidant content, like blueberries; they are rich in anthocyanins that are good for our cells.
Going onto the Genetic engineering details
The team expressed two transcription factors in tomatoes that do not exist in the wild type. Transcription factors are small molecules that find DNA activating it. They expressed the transcription factors Delila (Del) and Rosea1 (Ros1) from snapdragons and also the E8 promoter, which is present widely in plants. Promoters are DNA regions where the DNA replication machinery binds to start DNA transcription.
Main results
Purple tomatoes with the Del/Ros transcription factors had delayed riping after breaker compared to the red fruit with no transgenic transcription factors. This was observed in fruits on the vine and postharvest storage, but they also observed reduced levels of fungal infection in both conditions (vine and storage).
For purple tomatoes, 49 days of storage was needed to observe 505 of the fruit softened, while the red counterparts were 50% soft after only 21 days. Complete collapse of the fruit was observed at ten weeks for purple fruits and five weeks for red fruit. This indicated that Del and Ros1 could double the tomato’s shelf life.
To test the susceptibility of the fruit to the pathogen, tomatoes that were intact and wounded were sprayed with a spore suspension of B.cinera. The purple tomatoes showed much fewer infection symptoms than their red counterparts.
This team, to ensure that the delayed riping and pathogen susceptibility were compared at the same developmental stage, they treated the purple tomatoes with VIGS (virus-induced gene silencing), which was just to silence the transgenic transcription factors (Del and Ros1). The half of the tomato that was red (with Ros1 and Del1 silenced) was softer than the blue half ad collapsed earlier. The red part was also more prone to infection by the grey mould pathogen. (figure below)
(A) VIGS-Del/Ros1tomato fruits showed reduced accumulation of anthocyanins in silenced areas (i, pictures taken 14 days after breaker). The red sectors showed quicker softening than purple sectors (ii, pictures taken 42 days after breaker). Purple sectors showed reduced susceptibility to B. cinerea 3 dpi (iii). Red sectors of VIGS-silenced tomatoes were more susceptible to B. cinerea 3 dpi (iv). All scale bars represent 2 cm.
Conclusion
Shelf life is important for improving food waste,
Increasing the content of anthocyanins in tomatoes significantly improves the shelf life of the fruit,
The concentration of anthocyanins is connected to the plant's susceptibility to be infected with grey mould (B.cinera) by changing the dynamics of spread of ROS during infection.
*Not all results from the research article were included here; only the main results were covered.
