Comparative analysis of plant isochorismate synthases reveals structural mechanisms underlying their distinct biochemical properties

Abstract

Isochorismate synthase (ICS) converts chorismate into isochorismate, a precursor of primary and secondary metabolites including salicylic acid (SA). SA plays important roles in responses to stress conditions in plants. Many studies have suggested that the function of plant ICSs is regulated at the transcriptional level. In Arabidopsis thaliana, the expression of AtICS1 is induced by stress conditions in parallel with SA synthesis, and AtICS1 is required for SA synthesis. In contrast, the expression of NtICS is not induced when SA synthesis is activated in tobacco, and it is unlikely to be involved in SA synthesis. Studies on the biochemical properties of plant ICSs are limited, compared with those on transcriptional regulation. We analyzed the biochemical properties of four plant ICSs: AtICS1, NtICS, NbICS from Nicotiana benthamiana, and OsICS from rice. Multiple sequence alignment analysis revealed that their primary structures were well conserved, and predicted key residues for ICS activity were almost completely conserved. However, AtICS1 showed much higher activity than the other ICSs when expressed in Escherichia coli and N. benthamiana leaves. Moreover, the levels of AtICS1 protein expression in N. benthamiana leaves were higher than the other ICSs. Construction and analysis of chimeras between AtICS1 and OsICS revealed that the putative chloroplast transit peptides (TPs) significantly affected the levels of protein accumulation in N. benthamiana leaves. Chimeric and point-mutation analyses revealed that Thr531, Ser537, and Ile550 of AtICS1 are essential for its high activity. These distinct biochemical properties of plant ICSs may suggest different roles in their respective plant species.

Salicylic Acid Biosynthesis in Plants

“…Another study presents strong evidence for the importance of ICS1 in Arabidopsis. When AtICS1 is expressed in N. benthamiana, a much higher enzymatic activity is observed than for any other plant ICS tested, confirming the importance of ICS1 in Arabidopsis SA accumulation (Yokoo et al, 2018). The avrPphB SUSCEPTIBLE3 (PBS3) enzyme has recently been shown to be responsible for the conversion of IC to SA.…”

“…However, WRKY transcription factors regulate a multitude of defense-related genes, such as PAL, which could also be responsible for this increase in SA (Liu et al, 2005(Liu et al, , 2018. Furthermore, it was shown that OsICS has a very low level of enzymatic activity compared to the Arabidopsis homolog (Yokoo et al, 2018). In addition, there is no published research associating OsICS with disease resistance in rice.…”

Transcriptome Analysis of Black and White Sesame Seed Reveals Candidate Genes Associated with Black Seed Development in Sesame (Sesamum Indicum)

“…SIN_1026689 is a WAT1-related protein; SIN_1006025 encodes isochorismate synthase, and SIN_1025056 encodes a betaglucosidase isoform. In plants, isochorismate synthase converts chorismate the last product in the shikimate pathway into isochorismate, a precursor of phylloquinone (vitamin K1) and salicylic acid [37]. In addition, the 17 candidate genes also included 2 chalcone synthase genes SIN_1018961 and SIN_1018959.…”

Transcriptome Profile Analysis of Twisted Leaf Disease Response in Susceptible Sugarcane with Narenga porphyrocoma Genetic Background

“…The SA, which is generally involved in the Also, we analyzed the specific biosynthesis genes in SA, JA and ET pathway, 24 respectively. In details, the phenylalanine ammonia-lyase, an enzyme of phenylalanine 25 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 ammonium lyase (PAL) pathway in SA synthesis (Yokoo et al, 2018), was increased in 1 expression at the pre-onset of Phoma sp. infection.…”

“…infection. The isochorismate synthase 1, which 2 involved in the synthesis of SA (Yokoo et al, 2018), showed lower expression level in 3 three stages of the susceptible cultivar (Table S1). In the JA pathway, 12-4 oxophytodienoate reductase, which catalyses the reduction of 10, 11-double bonds of (Table S1).…”