The Erwinia chrysanthemi pecT gene regulates pectinase gene expression

Abstract

A new type of Erwinia chrysanthemi mutant displaying a derepressed synthesis of pectate lyase was isolated. The gene mutated in these strains, pecT, encodes a 316-amino-acid protein with a size of 34,761 Da that belongs to the LysR family of transcriptional activators and presents 61% identity with the E. coli protein LrhA. PecT represses the expression of pectate lyase genes pelC, pelD, pelE, pelL, and kdgC, activates pelB, and has no effect on the expression of pelA or the pectin methylesterase genes pemA and pemB. PecT activates its own expression. The mechanism by which PecT regulates pectate lyase synthesis is independent of that of the two characterized regulators of pectate lyase genes, KdgR and PecS. In contrast to most of the members of the LysR family, pecT is not transcribed in a direction opposite that of a gene that it regulates. pecT mutants are mucoid when grown on minimal medium plates and flocculate when grown in liquid minimal medium, unless leucine or alanine is added to the medium. Thus, pecT may regulate other functions in the bacterium.The synthesis and secretion of plant cell wall-degrading enzymes have been identified as one of the causes of the pathogenicity of Erwinia chrysanthemi (1). This plant pathogen is able to provoke the soft rot of a number of vegetable crops in the field or during storage. E. chrysanthemi 3937 has developed a set of enzymes to degrade pectin: two pectin methylesterases (encoded by the pemA and pemB genes) (21, 39), five major isoenzymes of pectate lyases (encoded by the pelA, pelB, pelC, pelD, and pelE genes), and at least four secondary pectate lyases. The gene of only one of them, pelL, has been cloned and studied (24). The action of these enzymes produces saturated and unsaturated oligogalacturonates that can be used as a carbon source and are metabolized by the products of the genes ogl, kduI, kduD, kdgK, and kdgA (11, 18, 33). The cellulolytic equipment of E. chrysanthemi is composed of the major, extracellular endoglucanase Z, the product of celZ (4), and of the periplasmic CelY protein, the product of celY (13).The regulation of the pel genes has been studied in vitro and in planta (23). Numerous factors influence the expression of the pel genes: growth phase (17), temperature, nitrogen starvation, oxygen concentration, osmolarity, the presence of rapidly metabolizable sugars (16), iron concentration (12), and the presence of plant extracts (5) or pectin and pectin catabolism products (8). This complexity led us to suppose that there are several regulatory proteins controlling pel gene expression. In contrast, expression of the genes of the intracellular part of the pectin degradation pathway seems to be inducible only by pectin degradation products (8), and no evidence of induction of the cel genes has been found up to now.The strategy used in our laboratory to study the regulation of the pectin degradation pathway has been to look for mutants synthesizing elevated levels of pectate lyases under uninduced conditions (17). With E. chrysanthemi 3937, this...

Regulation of type 1 fimbriae synthesis and biofilm formation by the transcriptional regulator LrhA of Escherichia coli

“…LrhA is closely related to HexA and PecT from plantpathogenic Erwinia species, which function as repressors both of motility and of multiple virulence factors, such as lytic exoenzymes (Harris et al, 1998;Surgey et al, 1996). However, neither haemolytic activity nor other established virulence factors of the UPEC strain 536, such as S or P fimbriae, appear to be significantly affected by LrhA.…”

Inactivation of pecS restores the virulence of mutants devoid of osmoregulated periplasmic glucans in the phytopathogenic bacterium Dickeya dadantii

“…Bacterial strains are described in Table 1. Bacteria were grown at 30 uC in either lysogeny broth (LB) (Bertani, 2004), minimal medium M63 supplemented with glycerol as a carbon source at a concentration of 2 g l 21 (Miller, 1992) or with polygalacturonate (PGA) as an inducer of pectate-lyase synthesis at a concentration of 4 g l 21 (Surgey et al, 1996). Solid media were obtained by adding 15 g agar l 21 .…”

“…This repression is likely to be suppressed in planta or when PGA is added to the medium, resulting in the accumulation in bacteria of 2-keto-3-deoxygluconate (KDG), a pectin degradation product and in planta inducer of KdgR (Nasser et al, 1992). The PecT transcriptional regulator is also known to repress the synthesis of pectinases (Surgey et al, 1996). In the kdgR single mutant strain, pectinases were constitutively expressed given that pectinase activities were similar after growth with or without PGA added and were similar to the pectinase activity observed for the wild-type strain grown with PGA added (Fig.…”

Characterization of the Erwinia chrysanthemi expI–expR locus directing the synthesis of two N‐acyl‐homoserine lactone signal molecules

“…In E. chrysanthemi, it has been demonstrated that the full expression of the pectin catabolism genes requires the presence of the cAMP-CRP complex Reverchon et al, 1997) and that the KdgR repressor essentially mediates the induction of these catabolic pathway genes by pectic compounds (Reverchon et al, 1991;Nasser et al, 1994). In addition to kdgR, two other loci involved in negative regulation of the pectinase gene expression, pecS-pecM and pecT, were also characterized in E. chrysanthemi, but the signal to which they respond still remains unknown (Praillet et al, 1996;Reverchon et al, 1994;Surgey et al, 1996;Castillo and Reverchon, 1997).…”