Generation of the salicylic acid deficient Arabidopsis via a synthetic salicylic acid hydroxylase expression cassette

Abstract

Background Salicylic acid (SA) is one of the plant hormones, which plays crucial roles in signaling transduction in plant growth, disease resistance, and leaf senescence. Arabidopsis (Arabidopsis thaliana) SA 3-hydroxylase (S3H) and 5-hydroxylase (S5H) are key enzymes which maintain SA homeostasis by catalyzing SA to 2,3-dihydroxybenzoic acid (DHBA) and 2,5-DHBA, respectively. Results SA deficient transgenic Arabidopsis lines were generated by introducing two binary vectors S5Hpro::EGFP-S3H and 35Spro::EGFP-S3H respectively, in which the expression of S3H is under the control of the S5H promoter or CaMV 35S promoter. Compared with the constitutive expression of S3H gene under the control of 35S promoter, the S3H gene under the native S5H promoter is activated by endogenous SA and results in a dynamic control of SA catabolism in a feedback mode. The SA accumulation, growth, leaf senescence, and pathogen resistance of the S5Hpro::GFP-S3H transgenic plants were investigated in parallel with NahG transgenic plants. The SA levels in the S5Hpro::EGFP-S3H transgenic plants were similar to or slightly lower than those of NahG transgenic Arabidopsis and resulted in SA deficient phenotypes. The low-SA trait of the S5Hpro::EGFP-S3H transgenic lines was inherited stably in the later generations. Conclusions Compared with NahG transgenic lines producing by-product catechol, S5Hpro::EGFP-S3H transgenic lines reduce SA levels by converting SA to a native product 2,3-DHBA for catabolism. Together, we provide new SA-deficient germplasms for the investigations of SA signaling in plant development, leaf senescence, and disease resistance.

Plant Synthetic Promoters

“…Cis-active elements are introduced according to their positions, copy number, distance, and orientation to promote optimum spacing among the cis-motifs and corresponding trans-factors, which could mutually interact and build functional dior oligomer complexes [182][183][184][185][186]188]. The prepared synthetic promoters demonstrate different tissue specificities, as well as strengths, and inducibility properties to precisely control the co-expression of numerous genes in complex biosynthesis traits [189][190][191][192][193][194]. In addition to the exchange of domains or cis-elements, novel synthetic promoter variants can also be prepared by the introduction of genetic changes into existing cis-active elements and core promoters [89,214].…”

“…The obtained promoters possess different tissue-specific, strength, and inducibility properties, enabling the co-expression of numerous genes at different levels, as is required by the complex biosynthesis traits or regulatory circuits responding to various environmental conditions, i.e., biotic, abiotic, tissue-specific, light stress, or hormonal stimulation [184,185,[189][190][191][192][193][194]. To avoid unwanted recombination or homology-dependent gene silencing, the expression of each gene is regulated by a different promoter [189,195].…”

“…The close spacing between cis-elements bound by trans-factors responding to SA and JA, or alternatively auxin or cytokinin treatment, allowed antagonistic pairs of plant regulators, such as JA/SA or auxin/cytokinin, to be studied. The obtained synthetic promoters could attenuate the antagonistic effects of the SA/JA and auxin/cytokinin pairs and strengthen responses to these stimuli [193]. Also, the feedbackregulated catabolism of SA to 2,3-dihydroxybenzoic acid, together with such physiologic effects as SA concentration in plant tissue, growth rate, leaf senescence, and pathogen resistance, was reconstructed in plants by the application of synthetic promoters containing the SA 3-hydroxylase (S3H) gene under the control of the SA-inducible promoter from SA 5-hydroxylase (S5H) [193].…”

“…The obtained synthetic promoters could attenuate the antagonistic effects of the SA/JA and auxin/cytokinin pairs and strengthen responses to these stimuli [193]. Also, the feedbackregulated catabolism of SA to 2,3-dihydroxybenzoic acid, together with such physiologic effects as SA concentration in plant tissue, growth rate, leaf senescence, and pathogen resistance, was reconstructed in plants by the application of synthetic promoters containing the SA 3-hydroxylase (S3H) gene under the control of the SA-inducible promoter from SA 5-hydroxylase (S5H) [193]. Furthermore, plant synthetic promoters based on the Q system from Neurospora crassa could not only be activated by the expression of QF2 and QF2w trans-factors but also constrained by the QS repressor, enabling the precise control of gene expression rate [234,235].…”

Plant Synthetic Promoters

“…Obtained promoters indicate different tissue-specific, strength, and inducibility properties to enable the co-expression of numerous genes at different levels, as is required by the complex biosynthesis traits or regulatory circuits responding to different environmental conditions, i.e., biotic, abiotic, tissue-specific, light-stress, or hormonal-stimulation conditions [184,185,[189][190][191][192][193][194]. To avoid unwanted recombination or homology-dependent gene silencing, the expression of each gene is regulated by a different promoter [189,195].…”