Plants can Skip the Middlemen to Directly Recognize Disease-Causing Fungi

Feb 20, 2019

Fungal diseases collectively termed powdery mildew afflict a broad range of plant species, including agriculturally relevant cereals such as barley, and result in significant reductions in crop yield. Fungi that cause powdery mildew deliver so-called effector molecules inside plant cells where they manipulate the host's physiology and immune system. In response, some plants have developed Resistance (R) genes, usually intracellular immune receptors, which recognize the infection by detecting the fungus' effectors, often leading to plant cell death at the site of attempted infection to limit the spread of the fungus. In the prevailing view, direct recognition of effectors by immune receptors is rather a rare event in plant-pathogen interactions, however, and it has been thought instead that in most cases recognition proceeds via other host proteins that are modified by the pathogen.

In barley populations, one of the powdery mildew receptors, designated mildew locus a (Mla), has undergone pronounced diversification, resulting in large numbers of different MLA protein variants with highly similar (>90%) DNA sequences. This suggests co-evolution with powdery mildew effectors, but the nature of the evolutionary relationship and interactions between immune receptor and effectors remained unclear.

To address these questions, Isabel Saur, Saskia Bauer, and colleagues from the department of Paul Schulze-Lefert first isolated several effectors from powdery mildew fungi collected in the field. Except for two, these proteins were all highly divergent from one another. When the authors expressed the effectors together with matching MLA receptors this led to cell death not only in barley but also in distantly related tobacco cells, already suggesting that no other barley proteins are required for recognition. Using bioluminescence as a marker for direct protein-protein interactions, the scientists indeed found specific associations of effector-MLA pairs in extracts of tobacco leaves. Similarly, a protein-protein interaction assay in yeast also revealed interactions only of matching effector-MLA pairs. These results suggest that highly sequence-related MLA receptor variants directly detect unrelated fungal effectors.

Click here to see more...

Video: Spring 2026 weather outlook for Wisconsin; What an early-arriving El Niño could mean

Northeast Wisconsin is a small corner of the world, but our weather is still affected by what happens across the globe.

That includes in the equatorial Pacific, where changes between El Niño and La Niña play a role in the weather here -- and boy, have there been some abrupt changes as of late.

El Niño and La Niña are the two phases of what is collectively known as the El Niño Southern Oscillation, or ENSO for short. These are the swings back and forth from unusually warm to unusually cold sea surface temperatures in the Pacific Ocean along the equator.

Since this past September, we have been in a weak La Niña, which means water temperatures near the Eastern Pacific equator have been cooler than usual. That's where we're at right now.

Even last fall, the long-term outlook suggested a return to neutral conditions by spring and potentially El Niño conditions by summer.

But there are some signs this may be happening faster than usual, which could accelerate the onset of El Niño.

Over the last few weeks, unusually strong bursts of westerly winds farther west in the Pacific -- where sea surface temperatures are warmer than average -- have been observed. There is a chance that this could accelerate the warming of those eastern Pacific waters and potentially push us into El Niño sooner than usual.

If we do enter El Nino by spring -- which we'll define as the period of March, April and May -- there are some long-term correlations with our weather here in Northeast Wisconsin.

Looking at a map of anomalously warm weather, most of the upper Great Lakes doesn't show a strong correlation, but in general, the northern tiers of the United States do tend to lean to that direction.

The stronger correlation is with precipitation. El Niño conditions in spring have historically come with a higher risk of very dry weather over that time frame, so this will definitely be a transition we'll have to watch closely as we move out of winter.