Two Novel Genes Induced by Hard-Surface Contact of Colletotrichum gloeosporioides Conidia

Abstract

Germinating conidia of many phytopathogenic fungi must differentiate into an infection structure called the appressorium in order to penetrate into their hosts. This differentiation is known to require contact with a hard surface. However, the molecular basis for this requirement is not known. Induction of this differentiation in the avocado pathogen, Colletotrichum gloeosporioides, by chemical signals such as the host's surface wax or the fruit-ripening hormone, ethylene, requires contact of the conidia with a hard surface for about 2 h. To study molecular events triggered by hard-surface contact, we isolated several genes expressed during the early stage of hard-surface treatment by a differential-display method. The genes that encode Colletotrichum hard-surface induced proteins are designated chip genes. In this study, we report the characterization of CHIP2 and CHIP3 genes that would encode proteins with molecular masses of 65 and 64 kDa, respectively, that have no homology to any known proteins. The CHIP2 product would contain a putative nuclear localization signal, a leucine zipper motif, and a heptad repeat region which might dimerize into coiled-coil structure. The CHIP3 product would be a nine-transmembrane-domain-containing protein. RNA blots showed that CHIP2 and CHIP3 are induced by a 2-h hard-surface contact. However, disruption of these genes did not affect the appressoriumforming ability and did not cause a significant decrease in virulence on avocado or tomato fruits suggesting that C. gloeosporioides might have genes functionally redundant to CHIP2 and CHIP3 or that these genes induced by hard-surface contact control processes not directly involved in pathogenesis.

A simple and effective method for total RNA isolation of appressoria in Magnaporthe oryzae

“…The concentration, 1.0×10 6 conidia/ml, was suitable for appressorium preparation and total RNA extraction, which was consistent with the previous reports (Kamakura et al, 1999;Irie et al, 2003). Substratum attachment appears to be a prerequisite for appressoriation of most fungi (Jelitto et al, 1994;Lee and Dean, 1994;Xiao et al, 1994;Kim et al, 2000), although conidium germination and appressorium formation are triggered by different signals in different species of phytopathogenic fungi. We found that duplicate film is a suitable substratum for conidium germination and appressorium formation in our experiments, because when inoculated with a high conidium population density, e.g., 1.0×10 6 conidia/ml, conidium germination and appressorium formation were nearly complete.…”

Nonpathogenic Strains ofColletotrichum lindemuthianumTrigger Progressive Bean Defense Responses during Appressorium-Mediated Penetration

“…We show here that mutant strain H18 is also unable to colonize plant tissues and to cause anthracnose symptoms when it is inoculated onto wounded plant surfaces. These data and data for other Colletotrichum species (25,42,43,53) suggest that in Colletotrichum species appressorium differentiation and maturation are compulsory developmental steps before colonization and degradation of host tissues. Consequently, if these steps do not take place, colonization does not occur even if the plant tissue surface is already mechanically broken.…”

The spore coat of the bean anthracnose fungus Colletotrichum lindemuthianum is required for adhesion, appressorium development and pathogenicity

“…Spore contact with a hard surface has been shown to be important for germination and/or appressorium formation for many fungal pathogens that infect the aerial parts of susceptible plants, e.g. the rice blast fungus Magnaporthe grisea [1], Botrytis cinerea [2] and the anthracnose fungi Colletotrichum gloeosporioides [3,4], C. trifolii [5], C. coccodes and C. dermatium [3]. Whether the surface is hydrophilic or hydrophobic can also affect germination and/or appressorium formation, e.g.…”

“…In some cases, chemical cues are also required for appressorium formation e.g. the avocado pathogen, C. gloeosporioides requires ethylene and avocado wax to trigger appressorium formation, but these are only effective after the spores have been in contact with a hard surface for 2 h [4,10]. Studies on Colletotrichum species and M. grisea have shown that genes encoding proteins involved in cell signalling, e.g.…”