Elucidating mechanisms of mycorrhiza-induced resistance against Thielaviopsis basicola via targeted transcript analysis of petunia hybrida genes.
One important function of the arbuscular mycorrhizal (AM) symbiosis is the protection of plants against pathogenic microorganisms, but little is known of the molecular background of mycorrhiza-induced resistance (MIR) in roots. Here, we investigated possible mechanisms responsible for reduced disease development in Funneliformis mosseae–colonized roots of Petunia hybrida after infection with the root rot pathogen Thielaviopsis basicola. Monitoring of the pathogenic fungus revealed that reduced symptoms in mycorrhizal root systems are not primarily based on increased disease tolerance, but rather on induced resistance. The presence of T. basicola did not affect mycorrhiza development immediately (24 and 36 hours after pathogen inoculation) but showed a slight negative influence after one week. AM induction of P. hybrida genes coding for nutrient transporters and defence-related genes was reduced by pathogen infection for some, but not all and only transiently, indicating that mycorrhiza functioning was maintained on the whole in pathogen-infected roots. In transcript profiling of 15 defence-related plant genes partially regulated by salicylic acid (SA) or jasmonate (JA) pathways, none showed expression resembling the phenomenon of priming usually accompanying JA-induced systemic resistance; several SA-regulated genes were down-regulated, when mycorrhizal roots were challenged with the pathogen. It is therefore proposed that mycorrhiza-intrinsic plant defence responses could establish a local barrier against root pathogens in mycorrhizal tissues. Expression patterns indicated a role of a basic endochitinase in these mycorrhiza-preformed barriers. Moreover, results suggested other oxilipins than jasmonate could be involved in signalling during interactions between the AM fungus and the pathogen in roots.
Hayek, S.; Gianinazzi-Pearson, V.; Gianinazzi, S.; Franken, P. 2014. Elucidating mechanisms of mycorrhiza-induced resistance against Thielaviopsis basicola via targeted transcript analysis of petunia hybrida genes. Physiological and Molecular Plant Pathology 88, 67-76.