Hexbyte Glen Cove The puzzle of nonhost resistance: why do pathogens harm some plants but not others? thumbnail

Hexbyte Glen Cove The puzzle of nonhost resistance: why do pathogens harm some plants but not others?

Hexbyte Glen Cove

People have puzzled for years why pathogen Phytophthora infestens causes the devastating late blight disease, source of the Irish Potato famine, on potatoes, but has no effect at all on plants like apple or cucumber. How are apple trees and cucumber plants able to completely shake off this devastating pathogen? Agricultural scientists have wondered for years: if this resistance is so complete and persists over so many generations, is there some way we could transfer it to susceptible plants like wheat and thereby stop disease?

Why is it so important to determine the molecular basis of nonhost resistance?

There are many examples of that are susceptible to one pathogen but able to resist another closely related pathogen. By uncovering the mechanism behind resistance, we can obtain a deeper understanding of the plant and can also uncover previously unknown aspects of immune signaling and regulation, which can help scientists improve resistance against a broader spectrum of .

This question has always been important as pathogens are a consistent threat to agriculture, limiting how much food is produced and where crops can be grown. Scientists continue to learn ways to reduce the impact of disease, through the development of pesticides, implementing new practices in the field, and breeding crops with enhanced resistance.

However, the modern world inadvertently undermines these efforts in a number of ways. Globalization and increased movement have contributed to the spread of pathogens into new environments. A prominent example is the recent emergence of wheat blast disease caused by the fungus Magnaporthe oryzae, which for a long time was unable to colonize wheat.

“The field of nonhost resistance sets out to identify novel ways to engineer resistance to these , guided by approaches that already exist in nature,” explained Matthew Moscou, a scientist at The Sainsbury Laboratory in Norwich, United Kingdom. “This question is fundamental to understanding why some plants get infected by a particular pathogen and others don´t, and, vice versa, why a given pathogen can only successfully colonize a limited number of plant species, which collectively form its host range.”

What do we know about nonhost resistance?

Scientists have learned that nonhost resistance is a feature controlled by many genes and largely governed by the characteristic attributes of a given plant-pathogen constellation. Pre-existing and induced physical barriers, such as the plant cuticle, and the secretion of antimicrobial molecules are often key factors in nonhost resistance. More recently scientists have recognized the interplay of host NLR-type immune sensors and secreted pathogen effector proteins as another important determinant of nonhost resistance.

What don’t we know about nonhost resistance?

“While the contribution of microbial commensals (microbes that naturally inhabit plant organs without causing any harm) to plant immunity has emerged during the past few years, their explicit role in nonhost resistance has not been demonstrated yet”, said Ralph Panstruga, a scientist at RWTH Aachen University in Germany. “Our knowledge on nonhost resistance largely relies on findings obtained in a handful of (model) angiosperm plant species that are genetically very tractable. We do not know yet to what extent these insights can be generalized, especially with respect to non-angiosperms.”

While there is a lot we don’t know about nonhost resistance, recent advances in technology, such as DNA sequencing methods, will make it easier for scientists to learn more. As for understanding the contribution of microbial commensals, scientists have recently been able to explore this aspect through reconstitution experiments with synthetic microbial communities in combination with germ-free plant systems. These tools were only recently established for some model plant species and are not yet available for many agriculturally important crops.

What can come from answering this question?

Learning more about nonhost resistance will help scientists better appreciate that susceptibility and resistance are the extreme outcomes of interactions between plants and pathogens, with all kinds of intermediate forms possible. Scientists may also discover undiscovered of plant pathogens on some species, which will enhance disease control strategies. Answering this question will also help scientists further comprehend whether microbial commensals contribute to resistance, which could form the basis for future plant protection measures. Finally, these insights will complete our picture of the plant immune system.

For the full review, read “What is the Molecular Basis of Nonhost Resistance?” published in the November issue of the MPMI journal. This article is the first in a series of ten reviews exploring the top 10 unanswered questions in molecular plant-microbe interactions, which came out of a crowdsourcing initiative spearheaded by the MPMI journal’s editorial board at the 2019 International Congress on Molecular Plant-Microbe Interactions in Glasgow, Scotland.

When meeting attendees Panstruga and Moscou heard about the quest to identify the top 10 unanswered questions in MPMI, they were immediately fascinated. When they saw the final list, they were drawn to the question about nonhost resistance, a plant defense that provides immunity to all members of a plant species against a microorganism that is harmful to other plant species.

“Since we both have published expertise in the area of nonhost resistance, it was somewhat self-evident that we could contribute with a review article to this relevant question,” said Panstruga. “We felt for quite some time that some concepts and terms in the field are ambiguous and possibly misleading, and that it would be just the right time to sum up the present knowledge, but also to clarify a few aspects and to raise a few fresh ideas.”



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Hexbyte Glen Cove Editorial: SoCal is losing its fight against smog. Things have to turn around in 2021 thumbnail

Hexbyte Glen Cove Editorial: SoCal is losing its fight against smog. Things have to turn around in 2021

Hexbyte Glen Cove

by The Times Editorial Board, Los Angeles Times, Distributed by Tribune Content Agency, LLC.

Credit: Unsplash/CC0 Public Domain

For a brief moment this year, Southern Californians got a glimpse of what clean air could look and feel like. During the first COVID-19 pandemic shutdowns in the spring, the dramatic drop in vehicle pollution combined with stormy weather to help clear out the region’s notoriously smoggy, hazy air, leaving blue skies and crisp vistas.

It didn’t last long. In fact, 2020 ended up being one of Southern California’s smoggiest years in decades, The LA Times’ Tony Barboza recently reported. There were 157 days when the region exceeded the federal health standard for ozone , the main ingredient in smog. That’s the most since 1997. The region has also had more than 30 days of excessive fine-particle pollution, or soot.

The overages weren’t a fluke. Southern California’s air quality has been on the decline for several years now, with the worst effects felt in San Bernardino, Riverside and other inland communities. Despite decades of emissions control regulations and programs, the region is losing the fight for clean air. Far too many residents still live with unhealthy levels of pollution that can permanently damage children’s lungs and raise adults’ risk of heart attacks and strokes.

The region will not meet a Clean Air Act deadline to reduce ozone levels by the end of 2022, which could lead to the loss of federal transportation funding and other penalties. Even more troubling, the trend line suggests Southern California will struggle to cut smog-forming emissions enough to meet a more stringent 2031 standard. The increase in unhealthful air appears to be linked to hotter weather—heat and sunlight transform certain pollutants into ozone—and smoke from wildfires. Climate change is driving both factors, and they’re only going to become more pronounced in the coming years.

Southern California has to turn the tide on air pollution. It won’t be easy, but 2021 will be a crucial year to adopt new regulations and policies that set the region on the course for clean air. The coming year will also test the South Coast Air Quality Management District, the region’s air quality regulator. The district’s governing board, which is made up of local elected officials, has too often bent to industry demands and delayed necessary regulations to cut emissions. Now those policies are coming up for a vote.

One of the most important regulations will target oil refineries. The proposed rule would get rid of an ineffective cap-and-trade-like system for curtailing refinery pollution and instead require these facilities to install the best available pollution control equipment. This proposal has been on the table for more than five years, but the oil industry has fought successfully to delay it—and it’s likely to lobby to weaken the current proposal. But the AQMD board has to realize there is no more time to waste. The rule, which would affect about 10 refineries, would cut more smog-forming emissions than any other regulation being considered by the district.

The AQMD board will also consider a first-of-its-kind regulation to cut pollution associated with warehouses. The goods movement industry is a huge source of emissions in the region, from diesel-belching at the ports of Los Angeles and Long Beach to the trucks and trains that haul containers to warehouses in the Inland Empire and beyond. The district has direct authority to regulate stationary sources of pollution, such as power plants, factories and refineries. But more than 80% of the region’s smog-forming pollution is created by vehicles, particularly diesel trucks, which are regulated by the state and federal governments.

Although the AQMD may not be able to regulate trucks directly, it can—and should—regulate facilities that are magnets for them. The proposed rule would require warehouses to reduce the emissions associated with their facilities by, for example, installing electric vehicle charging stations, buying low-emission or zero-emission equipment and encouraging their freight customers to use clean trucks. Again, the proposal is likely to face strong pushback from the logistics industry. But the AQMD board shouldn’t be swayed. E-commerce has boomed during the pandemic. This is an industry that can afford to pay more to help clean the air it is tainting in the smoggiest region of the country.

Likewise, the ports of Los Angeles and Long Beach delayed implementation of a fee on cargo that was supposed to help pay for cleaner trucks, citing the economic uncertainty of the pandemic. The ports now have record traffic; there’s no reason to wait on the fee or the transition to cleaner transport.

Southern California cannot solve its smog problem alone. The California Air Resources Board and the U.S. Environmental Protection Agency are crucial partners because they regulate the region’s biggest polluters. The EPA under the Trump administration largely abandoned its clean-air responsibilities; we hope the incoming Biden administration will recognize how much Southern California needs an ally in the effort to shift to a zero-emissions future.

We’ve seen how beautiful that future can be. Regulators need to step up to help make it a reality.



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