Biochemical and molecular responses of host plants to mycorrhizal infection and their roles in plant defence

Arbuscular mycorrhizas are most important symbioses in terrestrial ecosystems and they enhance the plant defence against numerous soil-borne pathogenic fungi, insect herbivores and nematodes. This paper reviews biochemical and molecular responses to arbuscular mycorrhizal infection. Arbuscular mycorrhizal fungal colonization leads to an array of biochemical and molecular responses in host plants: (i) increased production of many allelochemicals (phenolic compounds, terpenes, alkaloids, essential oils and other secondary compounds), (ii). induction of plant defence related genes [phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS) and chitinase coding genes] and (iii) activation of jasmonates signaling pathway. Biochemical and molecular responses to mycorrhizal infection play a vital role in mycorrhizal induced defence in host plants.