Differential accumulation of plant defense gene transcripts in a compatible and an incompatible plant-pathogen interaction.

Abstract

Phenylalanine ammonia-lyase and chalcone synthase catalyze the first reaction of phenylpropanoid biosynthesis and the first reaction of a branch pathway specific for flavonoid-isoflavonoid biosynthesis, respectively. These enzymes are key control elements in the synthesis of kievitone, phaseollin, and related isoflavonoidderived phytoalexins. RNA blot hybridization with 32P-labeled cDNA sequences was used to demonstrate marked accumulation of phenylalanine ammonia-lyase and chalcone synthase mRNAs in excision-wounded hypocotyls of Phaseolus vulgans L. (dwarf French bean) and during race-cultivar-specific interactions between hypocotybls of P. vulgans and the partialiy biotrophic fungus CoUetotrichum lindemudtianum, the causal agent of anthracnose. In an incompatible interaction (host resistant), early concomitant accumulation of phenylalanine ammonia-lyase and chalcone synthase mRNAs, loalized malnly but not entirely in tissue adjacent to the site of infection, was observed prior to the onset of phytoalexin accumulation and expression of localized, hypersensitive resitance. In contrast, in a compatible interaction (host susceptible) there was no early accumulation of these transcripts; instead, there was a delayed widespread response associated with phytoalexin accumulation during attempted lesion limitation. Two-dimensional gel electrophoresis of [S]methionine-labeled polypeptides synthesized in vitro by translation of isolated polysomal RNA demonstrated stimulation of the synthesis of characteristic sets of phenylalanine ammonia-lyase and chalcone synthase isopolypeptides in directly infected tissue and distant, hitherto uninfected tissue in both compatible and incompatible interactions. Our data show that specific accumulation of plant defense gene tanscripts is a key early component in the sequence of events leading to expression of defense responses in wounded tissue and in infected tissue during race-cultivar-specific interactions and that an elicitation signal is transmitted intercellularly in response to infection.

Differential regulation of a hydroxyproline-rich glycoprotein gene family in wounded and infected plants.

“…In a genetically incompatible interaction after fungal penetration of the first epidermal cell, there is a marked early induction of defense gene transcripts in tissue directly underlying the site of spore inoculation, correlated with expression of localized hypersensitive resistance and complete inhibition of further fungal growth (6,28). Moreover, transcription of defense genes is also stimulated at a distance in uninfected tissue, associated with the establishment of induced immunity and protection from subsequent attack by normally virulent pathogens.…”

“…Moreover, studies with cell cultures cannot provide information on the spatial orchestration of defenses in relation to localized damage or pathogen ingress. Therefore, we have extended the analysis from elicitor-treated cells to examine the activation of defense genes in bean hypocotyls in response to mechanical wounding and during race-cultivar-specific interactions with the fungus Colletotrichum lindemuthianum, the causal agent of anthracnose (5, 6,28).…”

Resistance gene-dependent plant defense responses.

“…Polygalacturonase-inhibiting proteins (PGIPs) inhibit PGs. PGlPs are induced in the bean-Colletotrichum lindemuthianum interaction with similar kinetics to pathogenesis-related (PR) proteins (Bell et al, 1986;Nuss et al, 1996). It has been hypothesized that PGlPs may retard PG function, which would lead to an elevated abundance of oligogalacturonides with a chain length of >8 units.…”

A Proteolytic Regulator Controlling Chalcone Synthase Stability and Flavonoid Biosynthesis in Arabidopsis

“…CHS gene expression and flavonoid biosynthesis are induced by a range of environment stimuli; in particular, the inducible synthesis of flavonoids plays a critical role in plant light responsiveness and UV damage protection (Ryder et al, 1984;Bell et al, 1986;Kaulen et al, 1986;Weisshaar et al, 1991;Thain et al, 2002). To explore whether the KFB CHS -mediated proteolysis of CHS also functions in the light-and/or stress-responsive synthesis of flavonoids, we first examined the transcriptional alteration of KFB CHS in the plants treated with white light.…”