Structural Diversity and Highly Specific Host-Pathogen Transcriptional Regulation of Defensin Genes Is Revealed in Tomato.

Defensins are small and rather ubiquitous cysteine-rich anti-microbial peptides. These proteins may act against pathogenic microorganisms either directly (by binding and disrupting membranes) or indirectly (as signaling molecules that participate in the organization of the cellular defense). Even though defensins are widespread across eukaryotes, still, extensive nucleotide and amino acid dissimilarities hamper the elucidation of their response to stimuli and mode of function. In the current study, we screened the Solanum lycopersicum genome for the identification of defensin genes, predicted the relating protein structures, and further studied their transcriptional responses to biotic (Verticillium dahliae, Meloidogyne javanica, Cucumber Mosaic Virus, and Potato Virus Y infections) and abiotic (cold stress) stimuli. Tomato defensin sequences were classified into two groups (C8 and C12). Our data indicate that the transcription of defensin coding genes primarily depends on the specific pathogen recognition patterns of V. dahliae and M. javanica. The immunodetection of plant defensin 1 protein was achieved only in the roots of plants inoculated with V. dahliae. In contrast, the almost null effects of viral infections and cold stress, and the failure to substantially induce the gene transcription suggest that these factors are probably not primarily targeted by the tomato defensin network.

A novel grapevine badnavirus is associated with the Roditis leaf discoloration disease.

Roditis leaf discoloration (RLD), a graft-transmissible disease of grapevine, was first reported in Greece in the 1980s. Even though various native grapevine viruses were identified in the affected vines, the etiology of the disease remained unknown. In the present study, we used an NGS platform for sequencing siRNAs from a twenty-year old Roditis vine showing typical RLD symptoms. Analysis of the NGS data revealed the presence of various known grapevine viruses and viroids as well as a hitherto uncharacterized DNA virus. The circular genome of the new virus was fully reassembled. It is 6988 nts long and includes 4 open reading frames (ORFs). ORF1, ORF2 and ORF4 code for proteins with unknown functions while ORF3 encodes a polyprotein with motifs related to the replication, encapsidation and movement of the virus. Phylogenetic analysis classified the novel virus within the genus Badnavirus, with closest relationship to Fig badnavirus 1. Further studies showed that the new badnavirus is closely related with the RLD disease and the provisional name grapevine Roditis leaf discoloration-associated virus (GRLDaV) is proposed. Our findings extend the number of DNA viruses identified in grapevine, further drawing attention to the potential importance of this virus group on grapevine pathology.