Co-silencing of tomato S-adenosylhomocysteine hydrolase genes confers increased immunity against Pseudomonas syringae pv. tomato DC3000 and enhanced tolerance to drought stress.

Xiaohui Li,Huijuan Zhang,Shixia Liu,Yafen Zhang,Yongbo Hong,Lei Huang,Fengming Song,Dayong Li

doi:10.3389/fpls.2015.00717

Xiaohui Li, Huijuan Zhang + Show 6 more

Open Access

https://doi.org/10.3389/fpls.2015.00717

Copy DOI

Abstract

S-adenosylhomocysteine hydrolase (SAHH), catalyzing the reversible hydrolysis of S-adenosylhomocysteine (SAH) to adenosine and homocysteine, is a key enzyme that maintain the cellular methylation potential in all organisms. We report here the biological functions of tomato SlSAHHs in stress response. The tomato genome contains three SlSAHH genes that encode SlSAHH proteins with high level of sequence identity. qRT-PCR analysis revealed that SlSAHHs responded with distinct expression induction patterns to Pseudomonas syringae pv. tomato (Pst) DC3000 and Botrytis cinerea as well as to defense signaling hormones such as salicylic acid, jasmonic acid and a precursor of ethylene. Virus-induced gene silencing-based knockdown of individual SlSAHH gene did not affect the growth performance and the response to Pst DC3000. However, co-silencing of three SlSAHH genes using a conserved sequence led to significant inhibition of vegetable growth. The SlSAHH-co-silenced plants displayed increased resistance to Pst DC3000 but did not alter the resistance to B. cinerea. Co-silencing of SlSAHHs resulted in constitutively activated defense responses including elevated SA level, upregulated expression of defense-related and PAMP-triggered immunity marker genes and increased callose deposition and H2O2 accumulation. Furthermore, the SlSAHH-co-silenced plants also exhibited enhanced drought stress tolerance although they had relatively small roots. These data demonstrate that, in addition to the functions in growth and development, SAHHs also play important roles in regulating biotic and abiotic stress responses in plants.

Highlights

S-adenosylhomocysteine hydrolase (SAHH) is a key enzyme in the activated methyl cycle and catalyzes the reversible hydrolysis of S-adenosylhomocysteine (SAH) to adenosine and homocysteine (Palmer and Abeles, 1979)
ESTs and putative full-length cDNAs for SlSAHHs were identified in the tomato genome database and NCBI GenBank database, respectively, indicating that SlSAHHs are constitutively expressed in tomato
The present study provides direct experimental evidence that integrates the biological functions of SAHHs into plant stress responses, in addition to the previously reported functions in growth and development

Summary

Introduction

S-adenosylhomocysteine hydrolase (SAHH) is a key enzyme in the activated methyl cycle and catalyzes the reversible hydrolysis of S-adenosylhomocysteine (SAH) to adenosine and homocysteine (Palmer and Abeles, 1979). The SAHH-catalyzed conversion of SAH into adenosine and L-homocysteine can release the SAH-caused feedback inhibition, which can promote further continual transmethylation reactions. The biological function of SAHH in animals has been studied in detail using specific inhibitors and genetic mutants. Direct evidence supporting the biological functions of SAHHs in plant growth and development came from recent genetic and biochemical studies using loss-of-function and gain-of-function mutants. Genome-wide analyses of gene expression and DNA methylation status in Arabidopsis SAHH mutant plants identified a large set of differentially expressed genes that are involved in pathways essential to plant growth and development and revealed DNA hypomethylation that is associated with gene silencing capabilities (Mull et al, 2006; Jordan et al, 2007; Li et al, 2008; Ouyang et al, 2012)

Methods

Results

Conclusion