Hot Weather Weakens Plant Immune System, Study Finds

Scientists have long been try­ing to under­stand why plants become more vul­ner­a­ble to dis­ease when tem­per­a­tures rise.

While rel­e­vant research is ongo­ing, a group of researchers from uni­ver­si­ties around the world sought ways to restore the plants’ abil­ity to defend against pathogens in hot weather.

“Plants get a lot more infec­tions at warm tem­per­a­tures because their level of basal immu­nity is down,” said Sheng-Yang He, a plant biol­o­gist at Duke University who led the research team. ​“So we wanted to know, how do plants feel the heat? And can we actu­ally fix it to make plants heat-resilient?”

The study, pub­lished in Nature, focused on Arabidopsis thaliana, an unas­sum­ing weed widely known as the mouse-ear cress, con­sid­ered the ​‘lab rat of plants’ by plant biol­o­gists. Arabidopsis thaliana thrives on road­sides, open paths and vacant lots and is used in exper­i­ments world­wide due to its short life cycle and short and easy-to-mod­ify genome.

The sci­en­tists said the main defense hor­mone of Arabidopsis thaliana is sal­i­cylic acid, which is used by many plants, includ­ing major crops, to resist dis­ease. However, the pro­duc­tion of sal­i­cylic acid can be dis­rupted when tem­per­a­tures rise a few degrees.

“Extreme weather con­di­tions asso­ci­ated with cli­mate change affect many aspects of plant and ani­mal life, includ­ing the response to infec­tious dis­eases,” the researchers wrote. ​“Production of sal­i­cylic acid, a cen­tral plant defense hor­mone, is par­tic­u­larly vul­ner­a­ble to sup­pres­sion by short peri­ods of hot weather above the nor­mal plant growth tem­per­a­ture range via an unknown mech­a­nism.”

After years of lab work, the researchers iso­lated the CBP60g gene, which can with­hold the pro­duc­tion of the sal­i­cylic acid hor­mone in plants when tem­per­a­tures rise, neu­tral­iz­ing their defense mech­a­nism. The solu­tion genet­i­cally bypassed the gene to restore the plan­t’s defense at hot­ter tem­per­a­tures.

“This was a multi-year and multi-insti­tu­tional effort,” Christian Danve Castroverde, a biol­o­gist at the Wilfrid Laurier University in Canada and co-author of the study, told Olive Oil Times.

“In 2013, [we] dis­cov­ered that short peri­ods of high tem­per­a­ture dra­mat­i­cally impact the hor­mone defenses of Arabidopsis plants against infec­tion by a bac­terium called Pseudomonas syringae,” he added. ​“After sev­eral more years, we were even­tu­ally suc­cess­ful in iden­ti­fy­ing the mol­e­c­u­lar basis of how Arabidopsis immu­nity is sup­pressed by warm tem­per­a­ture con­di­tions.”

The researchers bypassed the gene in the lab by adding a ​‘pro­moter.’ The short DNA sequence forces the gene to tran­scribe (copy the DNA sequence into an RNA mol­e­cule), restor­ing Arabidopsis thaliana’s abil­ity to pro­duce the sal­i­cylic acid hor­mone.

“Including the sal­i­cylic acid recep­tor and biosyn­thetic genes, opti­mized CBP60g expres­sion was suf­fi­cient to broadly restore sal­i­cylic acid pro­duc­tion, basal immu­nity and effec­tor-trig­gered immu­nity at the ele­vated growth tem­per­a­ture with­out sig­nif­i­cant growth trade-offs,” the researchers wrote.

The team has started test­ing gene mod­i­fi­ca­tion on food crops such as rape­seed. They also plan to exper­i­ment with more crops, includ­ing wheat and pota­toes. However, Castroverde said a sig­nif­i­cant amount of field research is required before apply­ing the fix at a large scale.

“Many plants have CBP60g-like genes, and a lot of them have the capac­ity to make sal­i­cylic acid,” he said. ​“It looks like plants already have a weapon in their arse­nal. Our chal­lenge now is just har­ness­ing this power. In terms of agri­cul­tural appli­ca­tions, I believe we have to wait until we have suc­cess­ful results in field tri­als.”

Nevertheless, the spe­cific solu­tion pro­posed by the research team to restore the plant immune sys­tem pre­sup­poses that con­sumers are ready to accept more genetic manip­u­la­tion of their food.

“As cli­mate change accel­er­ates, we’re going to be under pres­sure to learn things in the lab and move them into the field faster,” said Marc Nishimura, an expert in plant immu­nity at Colorado State University, who was not involved in the research. ​“I can’t see how we’re going to do this with­out more accep­tance of genet­i­cally mod­i­fied plants.”

Another study pub­lished by researchers at the Chinese University of Hong Kong in June warned that crop yields could decrease by 20 per­cent glob­ally by 2050 due to ozone pol­lu­tion and the effects of cli­mate change

Despite their suc­cess in restor­ing the Arabidopsis thaliana’s defense against heat, the researchers stressed the fact that the gap in under­stand­ing how a warm­ing cli­mate influ­ences the effec­tive­ness of the plant immune sys­tem is ​“a key con­cern for future agri­cul­tural pro­duc­tiv­ity, ecosys­tem preser­va­tion and the emer­gence of new plant dis­ease pan­demics.”

However, they added that their results point to crops becom­ing more resis­tant in the future.

“We were able to make the whole plant immune sys­tem more robust at warm tem­per­a­tures,” said He, the plant biol­o­gist from Duke. ​“If this is true for crop plants as well, that’s a really big deal because then we have a very pow­er­ful weapon.”

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