Plant pathogens cause up to 30% of crop yield losses worldwide, making it crucial to understand how to make plants more resistant to infection. A team of researchers has uncovered the critical role of a linker histone protein, called H1, during plant immune responses to bacterial and fungal infections. This fundamental knowledge could help generate smart crops that are resistant to multiple infectious agents simultaneously.
Linker histone and its role in infection regulation
Linker histones are known to regulate infection in animals, but their role in plant infection and immunity has never been explored. In animal and plant cells, fundamental units called nucleosomes contain DNA wrapped around a protein complex, which is critical for regulating genetic information. The individual nucleosomes are connected by linker DNA. Linker histone H1 holds the exit/entry site of linker DNA like a clip, thus regulating the unwinding and flexibility of nucleosomes. In plants like Arabidopsis, there are three isoforms of H1, and it suppresses gene expression, including the defense genes of the immune system.
Mutant Arabidopsis plants with all three H1 isoforms knocked out
The team explored mutant Arabidopsis plants with all three H1 isoforms knocked out. They grew wild-type and mutant plants under controlled conditions and then infected them with either the bacterial pathogen Pseudomonas syringae or the fungal pathogen Botrytis cinerea. After three days, they compared the severity of infection between the different groups of plants. The mutant plants were resistant to both bacterial and fungal infection when compared to wild-type plants, and the knockout mutant had higher levels of defense gene expression and the immune response hormone salicylic acid.
H1's role in defense priming
Probing H1's role further, the team were surprised to find that the mutant plants lacked defense-priming ability. In other words, when subjected to a small dose of a pathogen some time after initial infection, the plants showed no enhanced immune response. Like vaccination, priming a plant with a small pathogen dose can boost its immunity. The lack of defense priming in the mutant plants suggests H1 plays a critical role in priming.
Implications for crop development
Understanding the role of H1 in plant immunity could inform the development of crops that are resistant to multiple pathogens. However, this study also serves as a cautionary warning that it is important to study both the direct and indirect effects of a given mutation in genetically modified plants. This research highlights the critical role of H1 in plant immunity and opens up new avenues for research into the development of smart crops.
Journal Information: Arsheed H Sheikh et al, Linker histone H1 modulates defense priming and immunity in plants, Nucleic Acids Research (2023). DOI: 10.1093/nar/gkad106