Browsing by Subject "Laccaria bicolor"

Nitrogen is usually the growth limiting nutrient in boreal forest soils. Most of the nitrogen is bound to organic fraction, and low bioavailability of nitrogen delimits plant growth in boreal forest soils. Amino acids are easily available nitrogen compounds and thus they are important nitrogen sources for soil microorganisms. Almost all boreal forest trees form mycorrhizal assoociations with fungi. Mycorrhizal fungi produce wide variety of enzymes which break down organic nitrogen compounds. So far there is little knowledge of amino acid mineralization mechanisms of ectomycorrhizal fungi. L-amino acid oxidase (LAO) catalyses the mineralization of amino acids to ammonium. The ectomycorrhizal fungi Hebeloma spp. and Laccaria spp. have been shown to possess LAO enzyme activities. It has been proposed that LAO is one of the nitrogen mineralization mechanisms in ectomycorrhizal fungi, but so far no LAO genes have been described from basidiomycete fungi. In this study the first LAO gene sequences from the basidiomycete fungus Hebeloma cylindrosporum was described. The RACE-PCR -method was used to determine the 3´ and 5´ end sequences of the cDNA of the LAO1 gene. Based on the obtained sequences, primers to isolate the genomic DNA and cDNA sequences of the LAO1 gene were designed. The structure of the LAO1 gene, which is composed of five exons and four introns, was determined. Binding site of nitrogen regulating protein was found from upstream region of LAO1-gene. The partial genomic DNA sequence of gene adjacent to LAO1-gene was also measured. In the L. bicolor genome the gene preceding the LAO1 gene has been annotated as a putative pyruvate decarboxylase. In this study the partial cDNA sequence of another LAO-homolog of H. cylindrosporum was also determined. The LAO gene from another basidiomycete fungus, Laccaria bicolor, was also recognised. The gene model of LAO gene of L. bicolor was unannotated in the NCBI database. Based on the phylogenetic tree of LAO-related protein sequences, the ancestral form of LAO gene has been duplicated. This study provides molecular biological information on the catabolic mechanisms of amino acids in ectomycorrhizal fungi. Ammonium ions, produced by ectomycorrhizal fungi, might be a significant source of nitrogen for plants and other soil microbes. It is possible that LAO is an important factor of nitrogen cycle in soils of boreal forests.