Salicylic Acid Accumulation Under O3 Exposure is Regulated by Ethylene in Tobacco Plants

Abstract

Ozone (O3), a major photochemical oxidant, induces leaf injury concomitant with salicylic acid (SA) synthesis. In pathogen-infected leaves, SA is synthesized via two pathways, involving phenylalanine or isochorismate. SA biosynthesis under O3 fumigation is not well understood. When we applied 14C-labeled benzoic acid (a precursor of SA in the pathway via phenylalanine) to O3-exposed tobacco leaves, it was effectively metabolized to SA. However, the activity and mRNA level of isochorismate synthase (ICS) were not increased. In contrast, ICS activity was increased in O3-exposed Arabidopsis thaliana L. These results suggest that SA is synthesized via benzoic acid from phenylalanine in O3-exposed tobacco leaves but via isochorismate in Arabidopsis. Ethylene is a plant hormone that promotes leaf damage in O3-exposed plants. During O3 exposure, transgenic plants with a phenotype of reduced O3-induced ethylene production accumulated less SA than did wild-type plants. O3 increased the activity of phenylalanine ammonia-lyase (PAL) and the transcript levels of the chorismate mutase (CM) and PAL genes in wild-type tobacco, but their induction was suppressed in the transgenic plants. These results indicate that ethylene promotes SA accumulation by regulating the expression of the CM and PAL genes in O3-exposed tobacco.

The phenylalanine pathway is the main route of salicylic acid biosynthesis in Tobacco mosaic virus-infected tobacco leaves

“…We have suggested that in ozone-exposed tobacco, SA is synthesized via the phenylalanine pathway rather than the isochorismate pathway; we came to this conclusion from the results of experiments in which we did not observe increases in tobacco ICS activity and ICS gene expression after ozone exposure and instead observed a remarkable elevation of PAL activity and PAL gene expression (Ogawa et al 2005). However, although the increase in SA levels in TMV-infected tobacco leaves has been extensively studied (Malamy et al 1990;Malamy et al 1992;Seo et al 1995), the isochorismate pathway has so far not been reported to contribute to SA synthesis in TMV-infected tobacco.…”

PROHIBITIN3 Forms Complexes with ISOCHORISMATE SYNTHASE1 to Regulate Stress-Induced Salicylic Acid Biosynthesis in Arabidopsis

“…A major mechanism of SA deployment is through its increased synthesis in 94 response to pathogens and abiotic stresses, such as treatments with UV-C light, high light 95 radiation, and ozone (Yalpani et al, 1994;Nawrath et al, 2002;Ogawa et al, 2005;Mateo 96 et al, 2006;Catinot et al, 2008;Garcion et al, 2008). Interestingly, the Enhanced Disease 97 Susceptibility 5 (EDS5) SA transporter in the chloroplast envelope of Arabidopsis is 98 necessary for stress-induced SA accumulation, possibly due to a regulatory coupling of SA 99 transport and synthesis (Serrano et al, 2013;Yamasaki et al, 2013).…”

Nitric oxide: promoter or suppressor of programmed cell death?

“…In ozone-induced HR-like cell death, NO accumulation preceded accumulation of ethylene, salicylic acid (SA) and leaf injury (Rao and Davis, 2001;Ogawa et al, 2005;Tamaoki, 2008). S-nitrosylation of methionine adenyl transferase1 (MAT1), which is involved in ethylene biosynthesis, inhibits ethylene production (Lindermayr et al, 2006).…”