Biosynthesis of salicylic acid in plants

Abstract

Salicylic acid (SA) is an important signal molecule in plants.Two pathways of SA biosynthesis have been proposed in plants. Biochemical studies using isotope feeding have suggested that plants synthesize SA from cinnamate produced by the activity of phenylalanine ammonia lyase (PAL). Silencing of PAL genes in tobacco or chemical inhibition of PAL activity in Arabidopsis, cucumber and potato reduces pathogen-induced SA accumulation. Genetic studies, on the other hand, indicate that the bulk of SA is produced from isochorismate. In bacteria, SA is synthesized from chorismate through two reactions catalyzed by isochorismate synthase (ICS) and isochorismate pyruvate lyase (IPL). Arabidopsis contains two ICS genes but has no gene encoding proteins similar to the bacterial IPL. Thus, how SA is synthesized in plants is not fully elucidated. Two recently identified Arabidopsis genes, PBS3 and EPS1, are important for pathogen-induced SA accumulation. PBS3 encodes a member of the acyl-adenylate/thioester-forming enzyme family and EPS1 encodes a member of the BAHD acyltransferase superfamily. PBS3 and EPS1 may be directly involved in the synthesis of an important precursor or regulatory molecule for SA biosynthesis. The pathways and regulation of SA biosynthesis in plants may be more complicated than previously thought.

Synthesis and role of salicylic acid in wheat varieties with different levels of cadmium tolerance

“…It is possible that the phenyl-propanoid and isochorismate pathways are integrated through a metabolic or regulatory grid in SA biosynthesis. The two routes may respond differently to stress conditions and depend on the plant species investigated [13]. In the present study, although the PAL activity increased in certain wheat lines, these changes can hardly explain the dramatic SA accumulations observed.…”

“…The phenyl-propanoid pathway uses Lphenylalanine, derived from chorismate, and synthesises SA via cinnamate, produced by 4 phenylalanine ammonia lyase (PAL), but chorismate can also be converted into SA via isochorismate catalysed by isochorismate synthases (ICS) [12]. Recent publications suggest that the bulk of SA detected after exposure to biotic or abiotic stress is also synthesized from isochorismate, suggesting that the phenyl-propanoid pathway is only responsible for the synthesis of a small percentage of the SA in these plants [13]. How this endogenous signal molecule is synthesized and regulated in response to abiotic stress in plants, especially in crop plants, therefore remains an open question.…”

Salicylic acid mediates the reduced growth of lignin down-regulated plants

“…SA biosynthesis may occur through either the isochorismate synthase (ICS) route or via benzoic acid derived from cinnamate (17). The fast-neutron-generated sid2-2 mutant of Arabidopsis contains an exon deletion in the gene encoding ICS (20) that is implicated in SA biosynthesis (18).…”

“…The potential relationship between SA levels and lignin is intriguing because SA is biosynthetically related to lignin (17). Two major routes have been proposed for SA biosynthesis in plants.…”

Changes in the Expression of Genes in Soybean Roots Infected by Nematodes

“…The increase in PR-1 protein suggests that there may be an increase in the level of salicylic acid. Interestingly, there are two different possible routes to salicylic acid production (Chen et al 2009). Salicylic acid is known as a signal molecule for defense against nematodes (Branch et al, 2004).…”