Plant roots secrete antimicrobial compounds in order to defend themselves. Moreover, root exudates play an important role in microbe attraction to the roots. It is well known that root exudates including, amino acids, sugars and phenolic compounds attract zoospores from different Phytophthora species.
The volatile secondary metabolites exuded by plant roots are a mixture of different chemical compounds among them; terpenes usually have a prominent portion in that mixture. They are synthesized from five-carbon isoprene units resulting in monoterpenes, sesquiterpenes, diterpenes, sesterpenes, triterpenes and carotenoids, while when they are modified by oxygenation or addition of methyl groups they are called terpenoids. The biological role of these secondary metabolites is still not clear. Terpenes have been shown to be involved in plant-plant and plant herbivore signaling. In addition, terpenes affect the fungal behavior.
The inhibitory mechanisms of terpenes against microorganisms
vary and they are not fully elucidated. In bacteria, the mechanisms of action include degradation of cell wall, disruption of cytoplasmic membranes, increased permeability and increased hydrolysis. The strategies that fungi employ in order to overcome terpenes is not well known either. It has been reported that ATP-binding cassette transporters are involved in efflux of terpenes from fungal cells conferring resistance to these volatiles.
Verticillium species are ascomycetes fungi responsible for the Verticillium wilt disease in a plethora of cultivated and wild plants. More than 200 plant species can be infected by V. dahliae for example cotton, tomato, sugar beets, and olive trees. Verticillium longisporum is a diploid species that has been arisen through hybridization between V. dahliae and unspecified ancestor species. Both species are able to form long-lived resting structures, microsclerotia, which are melanised and compacted structures. The presence of host roots triggers the microsclerotia germination through a still unknown mechanism. V. dahliae causes typical wilt symptoms on tomato plants, while the symptoms that V. longisporum incites on B. napus are stunting, chlorosis and premature senescence. Interestingly, V. longisporum displays a preference to Brassicaceae plants.
The aim of this project is to investigate the transcriptome changes that terpenes can cause on V. longisporum using RNA-seq analysis.