Molecular perspectives on age-related resistance of plants to (viral) pathogens

Local Application of Acibenzolar-S-Methyl Treatment Induces Antiviral Responses in Distal Leaves of Arabidopsis thaliana

Systemic acquired resistance (SAR) is a plant defense mechanism that provides protection against a broad spectrum of pathogens in distal tissues. Recent studies have revealed a concerted function of salicylic acid (SA) and N-hydroxypipecolic acid (NHP) in the establishment of SAR against bacterial pathogens, but it remains unknown whether NHP is also involved in SAR against viruses. We found that the local application of acibenzolar-S-methyl (ASM), a synthetic analog of SA, suppressed plantago asiatica mosaic virus (PlAMV) infection in the distal leaves of Arabidopsis thaliana. This suppression of infection in untreated distal leaves was observed at 1 day, but not at 3 days, after application. ASM application significantly increased the expression of SAR-related genes, including PR1, SID2, and ALD1 after 1 day of application. Viral suppression in distal leaves after local ASM application was not observed in the sid2-2 mutant, which is defective in isochorismate synthase 1 (ICS1), which is involved in salicylic acid synthesis; or in the fmo1 mutant, which is defective in the synthesis of NHP; or in the SA receptor npr1-1 mutant. Finally, we found that the local application of NHP suppressed PlAMV infection in the distal leaves. These results indicate that the local application of ASM induces antiviral SAR against PlAMV through a mechanism involving NHP.

An efficient grafting method for phytoplasma transmission in Catharanthus roseus

BACKGROUND

Phytoplasmas are parasitic plant pathogens that reside intracellularly within the sieve tube cells. Phytoplasmas induce various symptoms, including floral virescence, phyllody, leaf yellowing, and witches'-broom. Currently, it is challenging to culture phytoplasma in vitro. In the laboratory, phytoplasmas are generally maintained in alternative host plants, such as Catharanthus roseus. Grafting is used to transmit phytoplasmas among the alternative hosts. During the experiment, scions from infected plants are grafted onto healthy plants using a side grafting method. However, the practice has certain limitations, including its inability to be applied to small plants and its irregular disease incidence.

RESULTS

Here, we demonstrate a new approach, penetration grafting, to overcome the limitations of side grafting. This grafting method allows phytoplasma to be efficiently and uniformly transmitted into the inoculated plants. No significant difference was observed in phytoplasma accumulation between both grafting techniques. However, penetration grafting allows rapid symptom development, saving waiting time and reducing space usage.

CONCLUSIONS

This study provides a reliable and stable method for experiments that require grafting transmission.