Identification of three ubiquitin genes of the rice blast fungus Magnaporthe grisea , one of which is highly expressed during initial stages of plant colonisation

Abstract

Differential cDNA screening was used to identify genes expressed during the colonisation of rice leaves by the pathogenic fungus Magnaporthe grisea. This led to the identification of a gene, called UEP1, which encodes a ubiquitin extension protein. UEP1 was highly expressed 48 h after initial fungal infection of rice leaves when M. grisea is proliferating in the leaf epidermis but not yet causing disease symptoms. UEP1 appeared to be down-regulated after this time despite further extensive growth of the fungus throughout the leaf tissue. To investigate the potential role of ubiquitin in fungal pathogenesis we subsequently isolated UEP3 and PUB4, encoding a second ubiquitin extension protein and a polyubiquitin respectively. UEP1 was expressed abundantly during active growth of M. grisea in axenic culture but was down-regulated by starvation-stress. UEP3 showed a similar pattern of expression to UEP1 during the growth of M. grisea in culture and after environmental stress, but was not highly expressed during plant colonisation. PUB4 was highly expressed after environmental stress, but was not highly expressed during plant colonisation. UEP1 was found to be present in a much-higher copy number per haploid genome compared to UEP3 and PUB4. The restricted high-level expression of UEP1 suggests that M. grisea undergoes rapid ribosomal biogenesis and protein turnover during initial plant-tissue colonisation, which is regulated by a specific UEP1-encoded component of the M. grisea ubiquitin gene family.

Gene Identification in the Obligate Fungal Pathogen Blumeria graminis by Expressed Sequence Tag Analysis

“…pombe have been identified (D00926) indicating active protein turnover during early B. graminis germling development. This notion is corroborated by similar observations during initial plant colonization by M. grisea (McCafferty and Talbot, 1998).…”

Multiubiquitin Chain Binding Subunit MCB1 (RPN10) of the 26S Proteasome Is Essential for Developmental Progression in Physcomitrella patens

“…This stress, in turn, could indirectly block differentiation. The ubiquitin/26S proteasome pathway is required for the stress response in many eukaryotes, and stressful conditions, such as growth on amino acid analogs, upregulates the synthesis of ubiquitin and other components of the pathway in yeast, animals, and plants (Finley et al, 1987;Burke et al, 1988;Feussner et al, 1997;Mathew et al, 1998;McCafferty and Talbot, 1998). The observation that the overall levels of free ubiquitin and ubiquitin chains are elevated in the ⌬mcb1 strains is congruent with this stress effect ( Figure 5A).…”

Susceptibility of rice to the blast fungus, Magnaporthe grisea

“…These studies have shown that an ubiquitin-encoding gene (UEP3) (McCafferty and Talbot, 1998), the gene encoding the mitochondrial small-subunit rRNA (Talbot and Tongue, 1998), and MPG1 encoding a class I hydrophobin, which is one of the most expressed M. grisea genes (Talbot et al, 1993), are strongly expressed during the colonization of the plant by the fungus. Since then, medium to large-scale expressed sequence tag (EST) projects as well as a SAGE analysis have allowed the discovery of novel M. grisea genes expressed during a susceptible infection using RNAs extracted from infected rice leaves (Kim et al, 2001;Rauyaree et al, 2001;Matsumura et al, 2003).…”