Mutualistic Fungal Endophytes Express a Proteinase that Is Homologous to Proteases Suspected to Be Important in Fungal Pathogenicity

Abstract

Many cultivated and wild grass species are hosts to mutualistic fungal endophytes. These associations are ecologically and agronomically significant, yet little is known regarding the physiological aspects of the interaction. In the Poa amp/a/Acremonium typhinum interaction, a fungal serine proteinase, Atl, is surprisingly abundant and may constitute 1 to 2% of the total leaf-sheath protein. Sequence analysis of cDNA and genomic clones indicates that proteinase Atl is a member of the eukaryotic subtilisin-like protease family. It is homologous to proteases suspected to be virulence factors in fungal pathogens of insects, nematodes, and other fungi. Cel blot analysis of RNA extracted from infected leaf-sheath tissue indicates that the proteinase Atl transcript leve1 is extremely high. RNA gel blots and immunoblots of purified enzymes indicate that similar proteinases are produced by Epichloe festucae and Acremonium lolii, the fungal endophytes infecting Festuca rubra subsp. rubra and Lolium perenne, respectively. Fungal expression of proteinase Atl-like enzymes may be a general feature of endophyte infection.

Peroxidase activity of perennial ryegrass and tall fescue seedlings artificially infected with endophytes

“…Our results show that e-endophytes, even introduced into novel hosts, do not generally enhance peroxidase activity. Reddy et al [23] reported that mutualistic fungal endophytes and some Epichloë species express a protease close to proteases suspected to be virulent factors in pathogen systems.…”

“…No specific pathogenicity or resistance mechanisms have been reported [12]. However, non-specific reactions from the fungus or the plant have been described; these reactions could explain some cases of incompatibility: i) Clavicipitaceous endophytes can express proteases homologous to other proteases involved in fungal pathogenicity of insects or nematodes [16,23]. Such proteases may facilitate colonisation of the host by degrading the plant cell wall and/or the apoplastic proteins providing a nutritional source for the fungus; ii) Endophyte infection can increase the expression of chitinase activity [24].…”

Expressed sequence tag (EST) analysis of two subspecies of Metarhizium anisopliae reveals a plethora of secreted proteins with potential activity in insect hosts

“…However, while it has been shown that these fungal pathogens share some enzymes involved in pathogenicity (Reddy et al, 1996), there is little overlap between plant and insect pathogens at the genus level. It follows that the characteristics needed by fungi to successfully establish disease in plants must be fundamentally different in some ways from those needed to infect animals.…”

“…We consequently adopted an EST strategy to assess pathogenicity determinants in On a wider scale, M. anisopliae belongs to the clavicipitaceous pyrenomycetes and is closely related to genera containing such well-known animal and plant pathogens as Fusarium, Trichoderma and Paecilomyces. However, while it has been shown that these fungal pathogens share some enzymes involved in pathogenicity (Reddy et al, 1996), there is little overlap between plant and insect pathogens at the genus level. It follows that the characteristics needed by fungi to successfully establish disease in plants must be fundamentally different in some ways from those needed to infect animals.…”

Interação entre Methylobacterium extorquens e cana-de-açúcar (Saccharum sp.)

“…Com esta colonização sistêmica da planta, estas bactérias podem alterar as condições fisiológicas e morfológicas do hospedeiro, além de atuar sobre as populações de outros microrganismos presentes no interior da planta (ANDREOTE et al, 2004;ANDREOTE et al, 2006). Entre as enzimas produzidas por estes microrganismos, podem ser citadas amilases (STAMFORD et al, 2001), exolevanases (MENENDEZ et al, 2002), quitinases (PLEBAN et al, 1997), glucanases (MOY et al, 2002) e proteases (REDDY et al, 1996), as quais podem atuar em processos importantes na interação microrganismo-planta.…”