Abstract
Madagascar periwinkle is an ornamental and a medicinal plant, and is also an indicator plant that is highly susceptible to phytoplasma and spiroplasma infections from different crops. Periwinkle lethal yellows, caused by Spiroplasma citri, is one of the most devastating diseases of periwinkle. The response of plants to S. citri infection is very little known at the transcriptome level. In this study, quantitative real-time PCR (RT-qPCR) was used to investigate the expression levels of four selected genes involved in defense and stress responses in naturally and experimentally Spiroplasma citri infected periwinkles. Strictosidine β-glucosidase involved in terpenoid indole alkaloids (TIAs) biosynthesis pathway showed significant upregulation in experimentally and naturally infected periwinkles. The transcript level of extensin increased in leaves of periwinkles experimentally infected by S. citri in comparison to healthy ones. A similar level of heat shock protein 90 and metallothionein expression was observed in healthy, naturally and experimentally spiroplasma-diseased periwinkles. Overexpression of Strictosidine β-glucosidase demonstrates the potential utility of this gene as a host biomarker to increase the fidelity of S. citri detection and can also be used in breeding programs to develop stable disease-resistance varieties.
Highlights
Known as the Madagascar periwinkle which belongs to the Apocynaceae family is one of the few medicinal plants that was mentioned in the folk medicinal literature as early as 2 BC, and is known to produce a large number of pharmaceutically valuable dimeric terpenoid indole alkaloids which are used in the treatment of hypertension and cancer
RT-qPCR for the four defense response genes was performed to explore the variance of gene expression between healthy, and naturally and experimentally, S. citri infected periwinkle leaves
Difference between treatments was considered as statistically significance when P < 0.05. These results provide evidence that strictosidine b-D-glucosidase and extensin are involved in the defense response in periwinkle against S. citri infection
Summary
Glycoside hydrolases have been classified into more than 100 families, based on amino acid sequence similarity They have various functions in cell wall metabolism and lignification, signaling and hydrolysis of starch, activation of chemical defense compounds against plant pathogens and herbivores [43,44,45,46,47]. They are up-regulated in response to salt, cold and osmotic stress in Arabidopsis [48]. For the first time we describe triscript analysis of four selected genes involved in plant stress and defense responses by RT-qPCR following infection by Spiroplasma citi. ,
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