The term epiphyte is used in general to characterize organisms that subsist only on plant surfaces. De Bar’s (1866) definition of endophytes—all the organisms that colonize internal plant tissues—was also used by Petrini (1986). In the same volume, Carroll (1986) restricted the use of the term endophyte to organisms that cause asymptomatic infections within plant tissues, excluding pathogenic fungi and mutualists such as mycorrhizal fungi. In view of the additional findings discussed in this chapter, however, I feel that this definition is no longer tenable. I propose, therefore, that Carroll’s definition be expanded to include all organisms inhabiting plant organs that at some time in their life, can colonize internal plant tissues without causing apparent harm to their host. This would account for those endophytic organisms that have a more or less lengthy epiphytic phase and also for latent pathogens that may live symptomless in their hosts for some time in their life.

Fungal Endophytes of Tree Leaves

Genetic engineering of filamentous fungi--progress, obstacles and future trends

Functional elements in the promoter region of the Aspergillus nidulans gpdA gene encoding glyceraldehyde-3-phosphate dehydrogenase.

The white rot basidiomycete Phanerochaete chrysosporium completely degrades lignin and a variety of aromatic pollutants during the secondary metabolic phase of growth. Two families of secreted heme enzymes, lignin peroxidase (LiP) and manganese peroxidase (MnP), are major components of the extracellular lignin degradative system of this organism. MnP and LiP both are encoded by families of genes, and the lip genes appear to be clustered. The lip genes contain eight or nine short introns; the mnp genes contain six or seven short introns. The sequences surrounding active-site residues are conserved among LiP, MnP, cytochrome c peroxidase, and plant peroxidases. The eight LiP cysteine residues align with 8 of the 10 cysteines in MnP. LiPs are synthesized as preproenzymes with a 21-amino-acid signal sequence followed by a 6- or 7-amino-acid propeptide. MnPs have a 21- or 24-amino-acid signal sequence but apparently lack a propeptide. Both LiP and MnP are regulated at the mRNA level by nitrogen, and the various isozymes may be differentially regulated by carbon and nitrogen. MnP also is regulated at the level of gene transcription by Mn(II), the substrate for the enzyme, and by heat shock. The promoter regions of mnp genes contain multiple heat shock elements as well as sequences that are identical to the consensus metal regulatory elements found in mammalian metallothionein genes. DNA transformation systems have been developed for P. chrysosporium and are being used for studies on gene regulation and for gene replacement experiments.

15 – Genetics and Molecular Biology of the Lignin-Degrading Basidiomycete Phanerochaete chrysosporium

This review focuses on three approaches used to study recombination mediated by cellular functions: (a) extrachromosomal recombination between transfected DNA molecules; (b) chromosomal recombination between repeated genes stably incorporated in the genome; and (c) targeted recombination between introduced DNA molecules and homologous sequences in the chromosome

J. R. S. Fincham

Papers

Transformation in fungi.