Lower incidence and severity of tomato virus in elevated CO₂ is accompanied by modulated plant induced defence in tomato

Abstract

Elevation in atmospheric CO(2) concentration broadly affects plant phenology and physiology, and these effects may alter the performance of plant viruses. The effects of elevated CO(2) on the susceptibility of tomato plants to Tomato yellow leaf curl virus (TYLCV) were examined for two successive years in open top chambers (OTC) in the field. We experimentally tested the hypothesis that elevated CO(2) would reduce the incidence and severity of TYLCV on tomato by altering plant defence strategies. Our results showed that elevated CO(2) decreased TYLCV disease incidence (by 14.6% in 2009 and 11.8% in 2010) and decreased disease severity (by 20.0% in 2009 and 10.4% in 2010). Elevated CO(2) also decreased the level of TYLCV coat protein in tomato leaves. Regardless of virus infection, elevated CO(2) increased plant height and aboveground biomass. Additionally, elevated CO(2) increased the leaf C:N ratio of tomato, but decreased soluble protein content in leaves. Notably, elevated CO(2) increased the salicylic acid (SA) level in uninfected and infected plants. In contrast, elevated CO(2) reduced jasmonic acid (JA) in uninfected plants while it increased JA and abscisic acid (ABA) in virus-infected plants. Furthermore, combined exogenous SA and JA application enhanced resistance to TYLCV more than application of either SA or JA alone. Our results suggest that the modulated antagonistic relationship between SA and JA under elevated CO(2) makes a great contribution to increased tomato resistance to TYLCV, and the predicted increases in tomato productivity may be enhanced by reduced plant virus susceptibility under projected rising CO(2) conditions.

Water Balance, Hormone Homeostasis, and Sugar Signaling Are All Involved in Tomato Resistance toTomato Yellow Leaf Curl Virus

“…Hence, overexpression of the JA-associated gene may be related to insect feeding rather than to virus infection per se. Moreover, combined applications of exogenous SA and JA induced stronger resistance to TYLCV than the application of either SA or JA alone (Huang et al, 2012). Therefore, it appears that the modulated interaction between SA and JA in the R line may significantly contribute to the observed TYLCV resistance.…”

“…Resistance to biotic stress is strongly associated with homeostasis of hormones such as SA and JA (Glazebrook, 2005;Thaler et al, 2010). Tomato plants grown in a CO 2 -enriched atmosphere exhibited increased resistance to the begomovirus TYLCV, as well as increased SA levels (Huang et al, 2012). Infection of Arabidopsis plants with the begomovirus Cabbage leaf curl virus (CaLCuV) led to an early pathogen response involving the SA pathway (Ascencio-Ibáñez et al, 2008).…”

“…SA and ABA have antagonistic effects. Thus, the ABA/SA cross talk will result in higher SA levels, leading to resistance to TYLCV (Huang et al, 2012).…”

“…Low levels of ABA can lead to high levels of SA due to antagonistic interactions between these two phytohormones (Audenaert et al, 2002; Mohr and Cahill, 2007;de Torres Zabala et al, 2009;Jiang et al, 2010). SA is well known for its role in resistance to numerous types of biotic stress (Hammond Kosack et al, 1996;Thomma et al, 1998), including geminiviruses (Ascencio-Ibáñez et al, 2008;Huang et al, 2012). This suggests that anisohydric resistance to biotic stress may be related to a plant defense mechanism regulated by ABA and SA.…”

“…It was recently shown (Huang et al, 2012) that tomatoes grown under elevated CO 2 show enhanced resistance to TYLCV and to Phytophthora parasitica, a phenomenon likely related to changes in SA/ABA levels (Jwa and Walling, 2001;Zavala et al, 2008). In addition, it has been previously demonstrated that in R plants in which LeHT1 has been silenced, hexoses are not taken up by the cells and, therefore, do not act as defense-signaling molecules, provoking the collapse of TYLCV resistance (Sade et al, 2013).…”