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The Impact of Elevated CO2 on Plant Pathogen Success

Paper Reviewed
Mhamdi, A. and Noctor, G. 2016. High CO2 primes plant biotic stress defenses through redox-linked pathways. Plant Physiology 172: 929-942.

Most CO2-enrichment studies are designed to examine the response of plants to familiar growth-related characteristics, such as photosynthesis or biomass. Few, however, have studied the susceptibility of plants under elevated levels of CO2 to pathogen attack. Investigating this latter phenomenon, and publishing their work in the journal Plant Physiology, was Mhamdi and Noctor (2016). Working with two ecotypes of thale cress (Arabidopsis thaliana), two bean varieties, and one variety of barley and wheat, the pair of French researchers explored "the potential impact of high CO2 on pathways involved in biotic stress resistance and related processes in plants" to see if elevated CO2 could provide any relief to pathogen stress.

In accomplishing their objective, they grew all plant species in controlled-environment chambers under three different CO2 concentrations (400, 1000 or 3000 ppm) for a period of three weeks, after which they infected them with either a virulent pathogen (Pseudomonas syringae pv tomato (Pto) DC3000) that typically gains entry into a plant via stomata, or a necrotrophic fungus (Botrytis cinerea B05.10) that can enter by penetrating the cuticle. And what did their experiment reveal?

As they describe it, they found that the "growth of plants in a CO2-enriched environment activates responses that are central to defense against pathogenic attack." In particular, salicylic acid accumulation in plant leaves was increased by 16.2- and 13.8-fold in the two thale cress ecotypes, by 5.1- and 4.3-fold in the two bean varieties, and by 1.7- and 1.6-fold in the wheat and barley plants, respectively (see figure below). Detailed analyses of thale cress further revealed that "elevated CO2 primes multiple defense pathways, leading to increased resistance to bacterial and fungal challenge" (emphasis added).

In light of these and other findings unreported here, Mhamdi and Noctor conclude that "high CO2 is sufficient to prime plant defenses through processes that are linked partly to redox signaling and metabolism, and this can decrease sensitivity to infection," while adding that "our data contribute to understanding the potential of plants to exploit the increased atmospheric CO2 concentrations that are predicted through the coming decades." And that is super good news for both people and plants!

Figure 1. Effects of high CO2 on the accumulation of SA in two Arabidopsis ecotypes (Columbia-0 [Col-0] and Wassilewskija [Ws]) and three different crop species. Numbers above the green bars indicate the fold change under CO2-enrichment conditions (1000 ppm) from ambient (400 ppm).

Posted 22 March 2017