Elevated CO₂ decreases the response of the ethylene signaling pathway in Medicago truncatula and increases the abundance of the pea aphid

Abstract

SummaryThe performance of herbivorous insects is greatly affected by plant nutritional quality and resistance, which are likely to be altered by rising concentrations of atmospheric CO 2 .We previously reported that elevated CO 2 enhanced biological nitrogen (N) fixation of Medicago truncatula, which could result in an increased supply of amino acids to the pea aphid (Acyrthosiphon pisum). The current study examined the N nutritional quality and aphid resistance of sickle, an ethylene-insensitive mutant of M. truncatula with supernodulation, and its wild-type control A17 under elevated CO 2 in open-top field chambers.Regardless of CO 2 concentration, growth and amino acid content were greater and aphid resistance was lower in sickle than in A17. Elevated CO 2 up-regulated N assimilation and transamination-related enzymes activities and increased phloem amino acids in both genotypes. Furthermore, elevated CO 2 down-regulated expression of 1-amino-cyclopropanecarboxylic acid (ACC), sickle gene (SKL) and ethylene response transcription factors (ERF) genes in the ethylene signaling pathway of A17 when infested by aphids and decreased resistance against aphids in terms of lower activities of superoxide dismutase (SOD), peroxidase (POD), and polyphenol oxidase (PPO).Our results suggest that elevated CO 2 suppresses the ethylene signaling pathway in M. truncatula, which results in an increase in plant nutritional quality for aphids and a decrease in plant resistance against aphids.

Plant stomatal closure improves aphid feeding under elevated CO2

“…By decreasing host resistance and increasing host amino acid concentration, elevated CO 2 enables stylet of the pea aphid to reach the M. truncatula phloem more easily and to consume more phloem sap (Guo et al ., , ,b). The increased phloem‐feeding phase, however, means that aphids must absorb more water from the xylem to balance the osmotic pressure of the hemolymph.…”

Net photosynthetic CO2 assimilation: more than just CO2 and O2 reduction cycles

“…This includes ACC synthase and the central transducer EIN2, with a close correlation with the CO 2 : O 2 ratio, suggesting that both ethylene synthesis and perception are enhanced at low photosynthesis (Supporting Information Table S1). Although the specific effect of gaseous conditions on ethylene synthesis is less documented than in fruits (where it is well‐known that CO 2 inhibits ethylene synthesis), available evidence indicates that in leaves, minimal carbon assimilation is required for carbon provision to ethylene synthesis (Grodzinski et al ., ; Guy & Kende, ) but increased CO 2 mole fraction (but not super‐high CO 2 ) inhibits ethylene synthesis (Guo et al ., ). ROS‐generating conditions (high photorespiration, low CO 2 : O 2 ratio) interact with ethylene signaling, as suggested by (1) the increased expression at low CO 2 of 2‐cysteine peroxiredoxin A (2CP A) within a few hours and (2) the fact that 2CP B contains a strong ethylene response element in its promoter (Heiber et al ., ).…”

Increased root herbivory under elevated atmospheric carbon dioxide concentrations is reversed by silicon‐based plant defences

“…; Martin & Johnson ), as well as other chemical changes such as alterations in the amino acid profile (Guo et al . ). Elevated CO 2 also causes suppression of the jasmonic acid pathway, which limits induced defences of plants against chewing herbivores (Ode, Johnson & Moore ).…”