CEVd-induced symptom modification as a response to a host-specific temperature-sensitive reaction.

Area of Science:

• Plant Pathology
• Virology
• Molecular Biology

Background:

• Citrus exocortis viroid (CEVd) exists as diverse variants.
• Viroid pathogenicity is linked to specific sequence and structural domains.
• Host-pathogen interactions can be influenced by environmental factors.

Purpose of the Study:

• To investigate the natural selection and stability of two CEVd variants.
• To characterize the differential symptomology induced by CEVd-S and CEVd-M in Gynura aurantiaca.
• To explore the underlying mechanisms of variable viroid-induced disease expression.

Main Methods:

• Observation of symptom severity in Gynura aurantiaca infected with CEVd variants.
• Propagation of viroid variants through cuttings and tissue extracts.
• Inoculation with cDNA clones of viroid variants.
• Molecular modeling to predict sequence and conformational changes.

Main Results:

• Two stable CEVd variants, CEVd-S (severe) and CEVd-M (mild), were identified.
• CEVd-S induced consistent severe symptoms, while CEVd-M caused variable symptoms, from asymptomatic to severe, particularly at 40°C.
• Differential host responses could not be correlated with sequence or conformational changes in the viroid variants.
• Variable symptom expression was linked to a temperature-sensitive response in Gynura aurantiaca.

Conclusions:

• CEVd variants can arise and maintain distinct pathogenic profiles.
• Gynura aurantiaca exhibits a temperature-sensitive response influencing CEVd-M symptom severity.
• Environmental factors, specifically temperature, play a crucial role in modulating viroid disease expression in susceptible hosts.