An Analysis of the Genomic Variability of the Phytopathogenic Mollicute Spiroplasma kunkelii

Abstract

Corn stunt disease has become a factor limiting maize production in some areas of the Americas in recent years. Although resistant maize genotypes have been developed in the past, this resistance has been unstable over time or in some geographical locations. To better understand disease components that could affect the stability of host resistance, we assessed the genome variability of the etiologic agent, Spiroplasma kunkelii. Isolates were obtained from a number of areas, and characterized molecularly by amplification of several regions of the spiroplasma chromosome and sequencing of specific gene fragments. The degree of polymorphism between isolates of different geographic origins was low, and the level of genomic variability was similar within isolates of different countries. Polymorphism among isolates was found in viral insertions and in the sequence of Skarp, a gene that encodes a membrane protein implicated in attachment to insect cells. The results suggest that the genome composition of this species is highly conserved among isolates. Hence, it is unlikely that the instability of maize resistance is due to generation of new pathotypes of S. kunkelii. Instead, other components of this complex pathosystem could account for the breakdown of resistance.

Characterization of components of resistance to Corn Stunt disease

“…One of the most convenient alternatives to reduce yield loss resulting from diseases is the use of resistant crops [29]. The resistance of maize genotypes to S. kunkelii might remain stable over time and across regions due to the low genomic variation of this pathogen [30]. Fieldresistant genotypes have in fact been obtained in areas of high pressure [31][32][33][34][35][36].…”

A Structural Framework for a Near-Minimal Form of Life: Mass and Compositional Analysis of the Helical Mollicute Spiroplasma melliferum BC3

“…This might explain the relatively large size of Spiroplasmas, their spatial organization and complexity compared to the Mycoplasmas. Spiroplasmas are of particular interest because they include agricultural pathogens of major economic importance such as S. citri affecting citrus plants [49] and S. kunkelii affecting corn [50], [51] , as well as members that have been claimed to be involved in neurodegenerative diseases [52]–[54]. However, we have a different motivation for studying Spiroplasma , namely our interest in establishing Spiroplasma as a model for analytically studying spatio-temporal, biomechanical and motility aspects of a minimal cell system [55].…”

The enemy within: phloem‐limited pathogens

“…Maize varieties resistant to corn stunt have been bred, but this resistance is short lived. It is unclear why maize resistance is quickly overcome, as genomic analysis has shown that S. kunkelii isolates have low genetic diversity (Carpane et al, 2013). Corn stunt is linked to magnesium metabolism: the symptoms are similar to magnesium deficiency, magnesium is involved in S. kunkelii localization and infected plants seem to be unable to process high magnesium concentrations (Nome et al, 2009).…”