Abstract
It has been previously described that elevation of endogenous spermine levels in Arabidopsis could be achieved by transgenic overexpression of S-Adenosylmethionine decarboxylase (SAMDC) or Spermine synthase (SPMS). In both cases, spermine accumulation had an impact on the plant transcriptome, with up-regulation of a set of genes enriched in functional categories involved in defense-related processes against both biotic and abiotic stresses. In this work, the response of SAMDC1-overexpressing plants against bacterial and oomycete pathogens has been tested. The expression of several pathogen defense-related genes was induced in these plants as well as in wild type plants exposed to an exogenous supply of spermine. SAMDC1-overexpressing plants showed an increased tolerance to infection by Pseudomonas syringae and by Hyaloperonospora arabidopsidis. Both results add more evidence to the hypothesis that spermine plays a key role in plant resistance to biotic stress.
Highlights
Polyamines (PAs) constitute a group of low molecular weight aliphatic amines, whose most widespread forms in living organisms are the diamine putrescine (Put), the triamine spermidine (Spd) and the tetraamine spermine (Spm)
PBISDCs TRANSGENIC LINES SHOW CONSTITUTIVE ELEVATED EXPRESSION LEVELS OF DISEASE RESPONSE AND JASMONIC ACID METABOLISM GENES Previous comparison of the transcriptomes of wild type (WT) and pBISDCs transgenic lines showed that overexpression of SAMDC1 gene in Arabidopsis leads to higher Spm levels and to the induction of a set of genes enriched in functional categories involved in defense-related processes against both biotic and abiotic stresses (Marco et al, 2011)
Expression levels of genes that encode for pathogenesis-related proteins PR-1 (AT2G14610), PR2 (AT3G57260) and PR-5 (AT3G57260) (Uknes et al, 1992; Van Loon et al, 2006); CYP79F1 (AT1G16410), a cytochrome P450 involved in the biosynthesis of aliphatic glucosinolates (Hansen et al, 2001; Chen et al, 2003); Cell-Wall associated kinase WAK1 (AT1G21245; Verica and He, 2002) as well as the flagellin receptor FLS2 (AT5G46330; Gomez-Gomez and Boller, 2000) were determined by Quantitative real time PCR (qRT-PCR) (Figure 1A)
Summary
Polyamines (PAs) constitute a group of low molecular weight aliphatic amines, whose most widespread forms in living organisms are the diamine putrescine (Put), the triamine spermidine (Spd) and the tetraamine spermine (Spm). PA biosynthesis pathway has been well characterized in A. thaliana (Alcazar et al, 2006) In this species, PA synthesis is initiated with Put synthesis from aminoacid arginine by the sequential action of arginine decarboxylase (ADC; EC 4.1.1.19), agmatine iminohydrolase (AIH; EC 3.4.3.12), and N-carbamoylputrescine amidohydrolase (CPA; EC 3.5.1.53). Decarboxylated Sadenosylmethionine (dcSAM) is used by both enzymes as donor molecule of aminopropyl groups, and is synthesized from the decarboxylation of S-adenosylmethionine (SAM) in a reaction catalyzed by SAM decarboxylase (SAMDC; EC 4.1.1.50). Characterization of the Arabidopsis genome has allowed to identify two genes encoding ADC (ADC1 and ADC2) (Watson and Malmberg, 1996; Watson et al, 1997) and one for each AIH and CPA (Janowitz et al, 2003; Piotrowski et al, 2003). The Arabidopsis genome carries two genes encoding SPDS (SPDS1 and SPDS2) (Hanzawa et al, 2002), one coding for SPMS (SPMS) (Panicot et al, 2002), another one coding for tSPMS (ACL5) (Knott et al, 2007; Kakehi et al, 2008), and at least four coding for SAMDC (SAMDC1-4) (Urano et al, 2003)
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