Lipopolysaccharides of Pectobacterium atrosepticum and Pseudomonas corrugata Induce Different Defence Response Patterns in Tobacco, Tomato, and Potato

Abstract

Lipopolysaccharides (LPS), ubiquitous cell surface components of Gram-negative bacteria, are directly implicated in plant/pathogen interactions. However, their perception by the plant, the subsequent signal transduction in both compatible and incompatible interactions, as well as the defence reactions induced in compatible interactions are as yet poorly understood. We focused on biochemical and physiological reactions induced in cell suspensions of three Solanaceae species (tobacco, tomato, and potato) by purified lipopolysaccharides from PECTOBACTERIUM ATROSEPTICUM (PA), a pathogen of potato, and PSEUDOMONAS CORRUGATA (PSC), a pathogen of tomato. LPS PA and LPS PSC caused a significant acidification of potato, tomato, and tobacco extracellular media, whereas laminarin (a linear beta-1,3 oligosaccharide elicitor) induced an alkalinisation in tobacco and tomato, but not in potato cell suspensions. None of the two LPS induced the formation of active oxygen species in any of the hosts, while laminarin induced H (2)O (2) production in cells of tobacco but not of tomato and potato. In tomato cells, LPS PA and LPS PSC induced a strong but transitory stimulation of lipoxygenase activity, whereas laminarin induced a stable or slightly increasing LOX activity over the first 24 h of contact. In tobacco, LOX activity was not triggered by either LPS, but significantly increased following treatment with laminarin. In potato, neither LPS nor laminarin induced LOX activity, in contrast with concentrated culture filtrate of PHYTOPHTHORA INFESTANS (CCF). These results demonstrate that LPS, as well as laminarin, are perceived in different ways by SOLANACEAE species, and possibly cultivars. They also suggest that defence responses modulated by LPS depend on plant genotypes rather than on the type of interaction.

Deciphering the dual effect of lipopolysaccharides from plant pathogenicPectobacterium

“…14,22 , 57 However depending on the plant species and the origin of the LPS, all did not induce an oxidative burst. 26,62 , 63 In our model, addition of DPI before elicitation altered the ROS generation by all LPS we tested, pointing out to a NADPH-oxidase-dependent pathway. Among the LPS preparations, those derived from Pectobaterium showed weaker ROS-generations compared to LPS from plant non-pathogenic bacteria, as previously described in rice cell culture.…”

“…26 One gram of lyophilized bacteria was suspended in 100 ml of cold distilled water and sonicated for 20 min in hot water at 65 C, before adding 100 ml of cold phenol 90 % (w/v). After a centrifugation (16 000 g, 45 min), the water phase was collected.…”

“…46 All LPS-containing fractions were pooled, dialyzed against distilled water, lyophilized, and tested for purity using the carbocyanine assay. 47 To confirm the presence of purified LPS a carbocyanine assay and SDS-PAGE electrophoresis was performed on the pooled fraction as described by Desender et al 26 LPS preparations were analyzed by SDS-PAGE in slab gels (4% polyacrylamide in stacking gel and 14% polyacrylamide in resolving gel) with the buffer system described by Laemmli. 48 After electrophoresis LPS were stained with silver nitrate 49 typical bands indicate the repeating units of oligosaccharide in the O antigen structure and the lipid A linked to the oligosaccharidic core (Fig.…”

“…9,[23][24][25] It was shown to induce different early responses such as acidification of the medium. 26 The fact that LPS induced variable cellular responses can be attributed to LPS preparations, plants and cell types used and reflect the ability of particular plants to recognize structural features within LPS that are not widely conserved. 14,27 [28][29][30] Also, depending on animal model and cell type, LPS could acts as mechanism of protection and preventing cell death, 31 or virulence factors by favoring the escape from the innate immune system.…”

“…57 However, the LPS Pa was reported to induce acidification of the extracellular medium of tomato culture cells when it failed to acidify potato extracellular medium. 26 The differential response to LPS from Pectobaterium and non-pathogenic bacteria is an additional indication on the ability of A. thaliana cells to display specific outcomes in response to the type of LPS origins. This difference is probably mediated by recognition of structural features within LPS that are not necessarily conserved between Pectobaterium and non-pathogenic bacteria.…”