‘Candidatus Phytoplasma zeae’: community-driven species delineation of the maize bushy stunt phytoplasma, a Dalbulus-transmitted corn pathogen confined to the Americas
TL;DR
The ecological profile of ‘Ca. P. zeae’, including its narrow host and vector range and restricted geographic distribution, supports its recognition as a novel species under Rule c of the IRPCM guidelines.
Abstract
Abstract A novel phytoplasma species, ‘Candidatus Phytoplasma zeae’, is proposed based on ecological distinctiveness, vector specificity, whole-genome comparisons and community consensus. This phytoplasma is associated with maize bushy stunt (MBS) disease in corn (Zea mays) and is transmitted exclusively by Dalbulus maidis and Dalbulus elimatus, two leafhopper species endemic to the Americas that has been reported in Brazil, Colombia, Mexico, Peru and several U.S. states. Here, we sequenced and assembled the genome of MBS phytoplasma (MBSP) strains from Brazil and the USA to describe and propose this new species. Although the 16S rRNA gene sequence of the proposed reference strain, MBSP-BRRS, shares >99% identity with that of ‘Candidatus Phytoplasma asteris’, key nucleotide polymorphisms distinguish ‘Ca. P. zeae’ from other 16SrI-related phytoplasma species. Genome-wide average nucleotide identity between ‘Ca. P. zeae’ and all available ‘Ca. P. asteris’-related strains genomes was between 92.6 and 98.4%. Comparative genomic analyses revealed unique gene clusters in ‘Ca. P. zeae’ associated with amino acid transport, defence mechanisms and protein turnover, which may contribute to its specialization in corn. The ecological profile of ‘Ca. P. zeae’, including its narrow host and vector range and restricted geographic distribution, supports its recognition as a novel species under Rule c of the IRPCM guidelines. The designation ‘Ca. P. zeae’ is, therefore, proposed by members of the research community who have studied this pathogen for over a decade, with the MBSP-BrazilRS strain serving as the reference.