Abstract
Rising atmospheric CO2 concentrations can affect the induced defense of plants against chewing herbivores but little is known about whether elevated CO2 can change the induced defense of plants against parasitic nematodes. This study examined the interactions between the root-knot nematode Meloidogyne incognita and three isogenic tomato (Lycopersicon esculentum) genotypes grown under ambient (390 ppm) and elevated (750 ppm) CO2 in growth chambers. In a previous study with open-top chambers in the field, we reported that elevated CO2 increased the number of nematode-induced root galls in a JA-defense-dominated genotype but not in a wild-type or JA-defense-recessive genotype. In the current study, we tested the hypothesis that elevated CO2 will favor the salicylic acid (SA)-pathway defense but repress the jasmonic acid (JA)-pathway defense of plants against plant-parasitic nematodes. Our data showed that elevated CO2 reduced the JA-pathway defense against M. incognita in the wild-type and in a genotype in which defense is dominated by the JA pathway (a JA-defense-dominated genotype) but up-regulated the SA-pathway defense in the wild type and in a JA-defense-recessive genotype (jasmonate-deficient mutant). Our results suggest that, in terms of defense genes, secondary metabolites, and volatile organic compounds, induced defense of nematode-infected plants could be affected by elevated CO2, and that CO2-induced changes of plant resistance may lead to genotype-specific responses of plants to nematodes under elevated CO2. The changes in resistance against nematodes, however, were small relative to those reported for chewing insects.
Highlights
Global atmospheric CO2 concentration has increased by approximately 40% from a pre-industrial value of 280 ppm to 387 ppm in 2009, and is anticipated to double by the end of this century [1]
Zavala et al (2009) showed that elevated CO2 down-regulated the gene expression and activity of cysteine proteinase inhibitors, which are the principal defenses of soybean against insect herbivores [7]
Our results show that in the jasmonate-deficient mutant spr2, elevated CO2 up-regulated the induced defense at 14-dpi based on the salicylic acid (SA) pathway, including PR1 and BGL2 genes, but did not up-regulate the induced defense based on the jasmonic acid (JA) pathway
Summary
Global atmospheric CO2 concentration has increased by approximately 40% from a pre-industrial value of 280 ppm to 387 ppm in 2009, and is anticipated to double by the end of this century [1]. Effects of elevated CO2 on nematode densities as mediated by the host plant are ‘‘plant species-specific’’ and include negative effects [10], positive effects [11], and no significant effects [12]. Most of these studies proposed that changes in root biomass and C/N ratio were the main factors responsible for the effects of elevated CO2 on nematode abundance [10,11,12]. The mechanisms underlying the effect of elevated CO2 on the interaction between plant-parasitic nematodes and their host plants are poorly understood
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