Master regulator of plant immunity

In plants, a regulatory protein associated with stress responses can also act as a master switch for immunity against pathogens, a demonstration that could help breeders develop crops that are more resistant to pests and better adapted to climates.

The kaust-led discovery suggests that agricultural scientists wishing to implement sustainable crop protection strategies can simply focus on this very important protein, rather than focusing on the individual immune signals involved in plant defense.

"Identifying OXI1 as a single-molecule switch for immunity offers many great advantages in molecular breeding," says Heribert Hirt, professor of plant science at KAUST and leader of the study.

Hirt's discovery took nearly 20 years. In 2004, he and his colleagues were the first to identify a species called OXI1—an abbreviation for oxidative signal-inducible kinase—that is critical for plant responses to environmental stress.

Over the next 18 years, Hirt and others linked OXI1 to various aspects of plant immunity and growth, but it wasn't entirely clear how the protein exerted its biological effects. While scientists have detailed how three key immune-related metabolites—salicylic acid (SA), n-hydroxyfruit acids (NHP) and camalexin—work on pathogen defense, the link between OXI1 Signal is unknown.

Hirt and Anamika Rawat, a postdoctoral researcher in his lab, connected the dots. The researchers created mutant forms of Arabidopsis plants that either lacked function or had elevated expression of the OXI1 regulatory protein. Then, together with collaborators in Germany and France, they comprehensively analyzed the patterns of gene activity, protein abundance and metabolite levels in these plants.

Collectively, the researchers showed how OXI1 triggers a number of genes that boost the synthesis of SA, NHP and camalexin. Accumulation of these three immunity-promoting molecules results in greater protection against plant pathogens.

But the extra immunity from OXI1 activity comes at a price: It makes plants stunted and display a greater propensity for cell death. Plants with low OXI1 levels, while more susceptible to infection by bacterial and fungal pests, tended to grow larger and have more active photosynthetic machinery.

Therefore, crop developers must find the appropriate balance of OXI1 activities for agricultural applications. As a protein kinase, OXI1 should be subject to manipulation, Hirt points out.

At present, dozens of small molecule drugs targeting kinases have been widely used in human medicine. Knowledge gleaned from the development of these formulations should now be used to discover modulators of Ox1 for crop improvement, he said.

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