Cacti fungal endophytes may help cacao tolerate drought
Key Points:
- The beans of Theobroma cacao are used to make chocolate and other products, but these plants are threatened by increased drought associated with climate change.
- Researchers identified microbes in drought-resistant plants, like cacti, that live in extreme environments and found 5 fungal endophytes, which live harmlessly inside plants, associated with drought tolerance.
- Cacao plants grown in soil enriched with these endophytes showed greater drought tolerance.
Washington, D.C.—Beans of the cacao plant, Theobroma cacao, are used in chocolates, pharmaceuticals and other products, but they’re under threat. Increased drought associated with climate change has already begun to stress cacao-growing regions of Colombia and other countries, and models predict it will get worse. In recent research, scientists have found that fungal endophytes—microbes that live in a host plant without causing harm—may offer a novel strategy for boosting drought tolerance in cacao.
For a study published this week in mSphere, mycologists added fungal endophytes from a species of cactus to the soil of growing cacao plants. They found that the inoculated plants showed less negative levels of leaf water potential, possibly due to better control of the stomatal conductance, which is a key determinant of photosynthesis. These alterations could help the plant retain more water as it grows.
“We are losing a lot of species due to climate change,” said Silvia Restrepo, Ph.D., senior author on the study and a plant pathologist at the Boyce Thompson Institute in Ithaca, New York, and the Universidad de los Andes in Bogotá, Colombia. The new study, she said, shows how scientists can harness strategies by looking for solutions that have evolved in other organisms.
Restrepo has long studied the effects of fungal endophytes, isolated from plants growing in extreme conditions in Colombia, on threatened crops. In previous work, her lab found endophytes that could improve the growth of potatoes. More recently, she said, she’s been working with cacao growers on drought resistance.
For the new work, she and her collaborators collected root samples in 2 locations in Colombia from 12 Stenocereus cacti, a tree-like genus characterized by its ability to thrive in arid, hot conditions. They isolated more than 20 fungal endophytes from the samples and subjected the fungi to drought conditions. Five of the isolates lost less than 20% of their total biomass. The researchers added these isolates to soil of growing cacao plants and compared them to cacao plants growing in ordinary soil, then subjected both to drought conditions.
The endophytes did not affect the height of the plants, but treated cacao plants developed more and larger leaves. In addition, plants inoculated with endophytes were better able to recover from the drought conditions. Endophytes from the genera Fusarium and Phoma also promoted plant growth under non-drought conditions.
Restrepo said scientists don’t know exactly why the endophytes help cacao with drought resistance. “The fine details are an open question,” she said. However, their analyses and observations suggest that the endophytes help the cacao plant manage the stomata, tiny pores that open and close to allow gas exchange, to avoid the rapid release of water vapor.
She suspects the endophytes may also confer similar benefits to other crops. “It’s easy to test in tomato, potato and other crops,” she said. Her group is also developing an endophyte-based soil additive that farmers could use to help their crops better survive drought in Colombia and beyond. “We have to look at all possibilities to help the crops fighting against climate change.”
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Journal
mSphere
How plants regulate their protein balance
International research team identifies cellular mechanism that maintains the stability of the plant proteome and controls stress responses
A specific cellular mechanism regulates the protein balance of plants, thereby influencing how they respond to environmental stress. A particular protein complex plays a key role in that process. It dynamically controls the degradation and recycling of proteins, a discovery made by an international research team led by Dr Markus Wirtz at the Centre for Organismal Studies of Heidelberg University. The investigations provide new insights into how this basic process – known as N-terminal acetylation – maintains the balance in protein turnover, thus contributing to the stability of the plant proteome.
Proteins are macromolecules made up of amino acids and have a variety of functions. For example, they serve as building blocks for cells, or, in the form of enzymes, can accelerate chemical reactions. For the growth, development, and survival of plants under changing environmental conditions, it is absolutely essential that the plant proteome – the totality of all proteins in an organism – remains in balance. To this end, proteins are constantly being synthesized, broken down, or recycled in a process known as proteostasis, explains Dr Xiaodi Gong, a postdoc in Dr Wirtz’ team.
In recent studies using the model plant organism thale cress, the research team gained new insights into how a fundamental cellular process regulates the degradation and recycling of proteins. A protein complex known as N-terminal acetyltransferase B (NatB) is of central importance here. It modifies approximately 20 percent of all proteins in eukaryotic cells by adding an acetyl group at a specific site. This process of N-terminal acetylation contributes to the regulation of protein balance.
As Markus Wirtz explains, NatB plays a much more dynamic role in determining the fate of proteins in this process than previously assumed in research. “We were able to show that the NatB protein complex marks certain proteins for degradation through the process of acetylation. Using this mechanism, the NatB complex regulates the activity of a protein kinase that controls protein recycling in plants,” says the scientist, who conducts research on physiological stress responses in plants at the Centre for Organismal Studies of Heidelberg University as part of the GreenRobust Cluster of Excellence.
To investigate this mechanism more closely, the researchers used genome editing to create plants in which the NatB protein complex was inactive. They observed a general decrease in protein turnover in these mutants. Quantitative analyses of the proteome also revealed that many proteins became more stable in the absence of NatB activity. This led to an accumulation of the protein kinase KIN 11, which is involved in the process by which plant cells recycle their components and recover nutrients under stress. Overall, the mutants that exhibited high KIN11 levels were significantly more resilient to a limited energy supply than untreated plants, particularly during prolonged darkness and the absence of photosynthesis.
Markus Wirtz: “Our findings establish NatB as a central regulator coordinating the interplay between protein degradation and recycling, thus contributing to the stability of the plant proteome.” At the same time, they demonstrate that a single biochemical modification is enough to fundamentally influence the stress response of plants. “A better understanding of these mechanisms opens up new avenues for basic research and also highlights ways to increase crop yields even under adverse conditions,” emphasizes the Heidelberg plant scientist.
Scientists from Université Paris-Saclay (France) and LMU Munich also participated in the research. The work was funded by the German Research Foundation and the French National Research Agency. The results were published in the journal “Nature Communications”.
Journal
Nature Communications
Article Title
The ribosome-associated N-terminal acetyltransferase B coordinates global proteostasis and autophagy in plants by creating Ac/N-degrons
