Purification and characterization of two basic beta-1,3-glucanases induced in Colletotrichum lindemuthianum-infected bean seedlings

Degradation of cellulose by the bean-pathogenic fungus Colletotrichum lindemuthianum. Production of extracellular cellulolytic enzymes by cellulose induction

Colletotrichum lindemuthianum was able to grow and produce extracellular cellulolytic activity in a defined medium containing cellulose as the main carbon substrate. As measured either by the hydrolysis of 4-methylumbelliferyl-beta-D -cellotrioside or the release of glucose from carboxymethylcellulose, activity reached a peak after 13 days of incubation and then declined whereas growth markedly increased afterwards. Detection of glucose in carboxymethylcellulose hydrolysates suggested the concerted operation of endo-1,4-beta-glucanase, cellobiohydrolase (exo-1,4-beta-glucanase) and beta-glucosidase activities. The highest levels of cellulolytic activity were obtained in media supplemented with cellulose and glutamate. Other carbon and nitrogen sources markedly influenced growth and enzyme production. Oligonucleotides homologous to specific regions of the cellobiohydrolase-encoding cbhII gene from Trichoderma reesei were used to isolate a C. lindemuthianum cbhII-DNA fragment whose sequence revealed homologies of 98% and 92% with the nucleotide and the deduced amino acid sequences of the corresponding cbhII-DNA of T. reesei, respectively. RT-PCR and Southern blot analyses of total RNA samples obtained from cellulose-grown but not from glucose-grown mycelium revealed the expression of the corresponding cbhII transcript. The cbhII-cDNA fragment was cloned and sequenced.

Phaseococcin, an antifungal protein with antiproliferative and anti-HIV-1 reverse transcriptase activities from small scarlet runner beans

From the seeds of small scarlet runner beans (Phaseolus coccineus 'Minor'), an antifungal protein with an N-terminal sequence homologous to those of defensins was isolated. The antifungal protein bound to Affi-gel blue gel and Mono S but it did not bind to DEAE-cellulose. It was further purified by gel filtration on a Superdex peptide column. It exhibited a molecular mass of 5422 Da as determined by mass spectrometry. The protein, designated as phaseococcin, suppressed mycelial growth in a number of fungi including Botrytis cinerea, Coprinus comatus, Fusarium oxysporum, Mycosphaerella arachidicola, Physalospora piricola, and Rhizoctonia solani. It also inhibited proliferation in several Bacillus species and the leukemia cell lines HL60 and L1210 and curtailed the activity of HIV-1 reverse transcriptase. It did not affect proliferation of mouse splenocytes and neither did it inhibit protein synthesis in a cell-free rabbit reticulocyte lysate system.Key words: antifungal proteins, runner beans, antiproliferative.

Elicitor activity of a fungal endopolygalacturonase in tobacco requires a functional catalytic site and cell wall localization

CLPG1, an endopolygalacturonase (endoPG) gene of Colletotrichum lindemuthianum, was transferred to tobacco (Nicotiana tabacum) leaves by using the Agrobacterium tumefaciens transient delivery system. The following four constructs were prepared: CLPG1, with or without its signal peptide (SP; PG1, PG1deltaSP); CLPG1 with the tobacco expansin1 SP instead of its own SP (Exp::PG1deltaSP); and a mutated version of the latter on two amino acids potentially involved in the catalytic site of CLPG1 (D202N/D203N). Chlorotic and necrotic lesions appeared 5 to 7 d postinfiltration, exclusively in response to CLPG1 fused to the expansin SP. The lesions were correlated to the production of an active enzyme. Necrosis-inducing activity, as well as endoPG activity, were completely abolished by site-directed mutagenesis. Ultrastructural immunocytolocalization experiments indicated that the expansin SP addressed CLPG1 to the cell wall. Staining of parenchyma cells revealed the progressive degradation of pectic material in junction zones and middle lamella as a function of time after infiltration, ultimately leading to cell separation. A 30% decrease in the GalUA content of the cell walls was simultaneously recorded, thereby confirming the hydrolytic effect of CLPG1 on pectic polysaccharides, in planta. The elicitor activity of CLPG1 was further illustrated by the induction of defense responses comprising active oxygen species and beta-1,3-glucanase activity, before leaf necrosis. Altogether, the data demonstrate that an appropriate SP and a functional catalytic site are required for the proper expression and elicitor activity of the fungal endoPG CLPG1 in tobacco.