Exploring laccase genes from plant pathogen genomes: a bioinformatic approach.

To date, research on laccases has mostly been focused on plant and fungal laccases and their current use in biotechnological applications. In contrast, little is known about laccases from plant pathogens, although recent rapid progress in whole genome sequencing of an increasing number of organisms has facilitated their identification and ascertainment of their origins. In this study, a comparative analysis was performed to elucidate the distribution of laccases among bacteria, fungi, and oomycetes, and, through comparison of their amino acids, to determine the relationships between them. We retrieved the laccase genes for the 20 publicly available plant pathogen genomes. From these, 125 laccase genes were identified in total, including seven in bacterial genomes, 101 in fungal genomes, and 17 in oomycete genomes. Most of the predicted protein models of these genes shared typical fungal laccase characteristics, possessing four conserved domains with one cysteine and ten histidine residues at these domains. Phylogenetic analysis illustrated that laccases from bacteria and oomycetes were grouped into two distinct clades, whereas fungal laccases clustered in three main clades. These results provide the theoretical groundwork regarding the role of laccases in plant pathogens and might be used to guide future research into these enzymes.

Molecular characterization and functional analysis of the Nep1-like protein-encoding gene from Phytophthora capsici.

Phytophthora capsici is an aggressive plant pathogen that affects solanaceous and cucurbitaceous hosts. Nep1-like proteins (NLPs) are a group of effectors found particularly in oomycetes and considered important virulence factors. We identified an NLP gene (phcnlp1) from the highly virulent P. capsici strain Phyc12 that had an encoded polypeptide of 476-amino acid residues and a predicted molecular mass of 51.75 kDa. We performed quantitative reverse transcription-polymerase chain reaction to detect the expression pattern of phcnlp1 during various phases of interaction with the host plant, and the results showed that phcnlp1 was increasingly expressed during symptom development after P. capsici infection of pepper leaves. We also confirmed that phcnlp1 caused significant necrosis on tobacco plants when expressed based on potato virus agroinfection. All results indicated that phcnlp1 belongs to the NLP gene family and is important for the pathogenesis of P. capsici in its hosts.

Identification of 18 genes encoding necrosis-inducing proteins from the plant pathogen Phytophthora capsici (Pythiaceae: Oomycetes).

Phytophthora capsici is an aggressive plant pathogen that affects solanaceous and cucurbitaceous hosts. Necrosis-inducing Phytophthora proteins (NPPs) are a group of secreted toxins found particularly in oomycetes. Several NPPs from Phytophthora species trigger plant cell death and activate host defense gene expression. We isolated 18 P. capsici NPP genes, of which 12 were active during hypha growth from a Phytophthora stain isolated from pepper (Capsicum annuum) plants in China. The 18 predicted proteins had a sequence homology of 46.26%. The 18 Pcnpp sequences had a conserved GHRHDWE motif and fell into two groups. Eleven sequences in group 1 had two conserved cysteine residues, whereas the other seven sequences in group 2 lacked these two cysteine residues. A phylogenetic tree was constructed on the basis of the alignment of the predicted protein sequences of 52 selected NPP genes from oomycetes, fungi and bacteria from Genbank. The tree did not rigorously follow the taxonomic classification of the species; all the NPPs from oomycetes formed their own clusters, while fungal sequences were grouped into two separate clades, indicating that based on NPPs, we can separate oomycetes from fungi and bacteria, and that expansion of the NPP family was a feature of Phytophthora evolution.