International team discovers small molecules that regulate how fast plant leaves age

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Two small molecules that are produced by the plant Arabidopsis thaliana are shown to have the opposite effect on how fast its leaves age. The molecules are peptides, short chains of amino acids. While the peptide SCOOP10 accelerates aging, SCOOP12 suppresses it. Together, these peptides are thought to regulate the aging process in plants.

An international team of scientists, including Utrecht University plant biologist Nora Gigli-Bisceglia, Christa Testerink from Wageningen UR and Yongfeng Guo and Zhenbiao Zhang from the Chinese Academy of Agricultural Sciences, demonstrates this in a publication in the journal Molecular Plant.

Potentially, simply spraying SCOOP12 on a field could delay the agriculturally undesired effects of aging in crop plants.

In the final stage of the life of a leaf, the contents of the leaf are broken down. As a result, the leaf turns yellow. And while this perhaps does not look like a good thing to us, in general this process of aging is actually beneficial for the plant, as it helps the plant to store and recycle nutrients that are needed for the production of seeds and fruits.

Environmental stresses

However, the process of the aging of plants, also called senescence, is an increasing problem in agriculture, says Gigli-Bisceglia.

"Aging is triggered by most environmental stresses, such as drought, high temperatures and high salinity of the soil. Under these conditions, the plants use senescence as an escape mechanism to recycle nutrients.

"Also, older tissues undergo senescence to protect the younger leaves. Ultimately, prolonged exposure to stress leads to excessive senescence and to plant death. Due to climate change, crop plants are increasingly experiencing such environmentally stressful conditions."

Delayed and accelerated aging

The team of scientists discovered the function of the two peptides after they realized that Arabidopsis-plants that lacked the receptor MIK2 showed early aging. MIK2 is a plant protein on the surface of plant cells that is known to interact with peptides from the SCOOP-family.

The researchers therefore decided to apply a range of SCOOP-peptides on detached leaves. To trigger aging, they placed the leaves in the darkness. They noticed that in some cases, like SCOOP10, leaves turned yellow faster than usual: in the case of SCOOP10, after three or four days, rather than the five days it takes for untreated leaves. But in other cases, like SCOOP12, leaves started yellowing only after more than seven days.

As a next step, the researchers created Arabidopsis-plants that were not able to produce the SCOOP10 and SCOOP12 peptides. Plants lacking SCOOP10 were found to show delayed aging. Even after 40 days, the plants remained green. In contrast, plants lacking SCOOP12 aged sooner than usual.

Regulation of aging

It was previously shown that SCOOP12 binds to the receptor MIK2. In the new paper, the researchers show that SCOOP10 also strongly binds to the same receptor. According to Gigli-Bisceglia, it is striking that the binding of each of these two peptides to the same receptor results in an opposite response.

The team also found that when SCOOP10 is bound to MIK2 and you add SCOOP12, the binding between SCOOP10 and MIK2 is lost.

Gigli-Bisceglia says, "These insights make us suspect that these two peptides compete to regulate aging in these plants. When it is time for the plant to start aging, SCOOP10 is produced. But at the same time, SCOOP10 triggers the production of SCOOP12. That is why we have hypothesized a scenario where SCOOP10 initiates the aging process, while SCOOP12 is the control to make sure aging does not go too fast."

Agriculture application

In theory, it would be possible to simply spray SCOOP12 or another SCOOP with a similar effect on crop fields to delay the aging process. Gigli-Bisceglia thinks this could potentially work for many crop plants, but especially those from the Brassicaceae-family, of which Arabidopsis is also a member. This family includes cabbage, kale, cauliflower and many other vegetables.

However, spraying peptides on crops is not a common practice in agriculture. "This is not because the peptides are harmful, but simply because they are expensive. But if spraying peptides became something that is done by everybody, the prices might drop. They are just small molecules that should not be very complicated to produce on a large scale," said Gigli-Bisceglia.

Gigli-Bisceglia adds that by using molecules that already occur naturally in plants, the expected impact on the environment is low, because these peptides are biodegradable, unlike many chemicals that are currently used.

Human aging

Human beings have been trying to defeat aging for a long time. Do the new results offer new opportunities for our species as well?

"Just like in plant cells, small peptides have been identified in animal cells. They exert many functions there, like regulating growth and development. And if you, for example, look at how innate immunity works in plants and in animals, the mechanisms have features that function in a similar way, including the activation of the defense responses by very similar receptors with very similar functions," said Gigli-Bisceglia.

"So, even though evidence is currently lacking and considering the obvious differences between animals and plants, we cannot exclude that animals have also evolved a mechanism that regulates cellular aging in a similar way to what we see in plants."

More information: Zhenbiao Zhang et al, SCOOP10 And SCOOP12 Peptides Act Through MIK2 Receptor-Like Kinase to Antagonistically Regulate Arabidopsis Leaf Senescence, Molecular Plant (2024). DOI: 10.1016/j.molp.2024.10.010

Journal information: Molecular Plant

Provided by Utrecht University