Abstract

RAMIREZ GOMEZ, Margarita  and  RODRIGUEZ, Alia. Plant defense mechanisms and responses in the arbuscular mycorrhizal symbiosis: a review. Rev. colomb. biotecnol [online]. 2012, vol.14, n.1, pp.271-284. ISSN 0123-3475.

Harmonic processes between plant and arbuscular mycorrhyzal fungi (AMF) are required for the symbiosis formation between the two organisms. These processes depend on specific signalling for the plant-fungus recognition, colonisation and bidirectional nutrient exchange. Plants show defence responses against invasive organisms, however they react weakly and localised when challenged by AMF. The benefits derived from the mycorrization are described for the nutritional aspect; however, it is known that mycorrhized plants are more tolerant to biotic stresses. Mycorrhizal induced resistance (MIR) is especially important for the control of foliar pathogens, leaf cutters and necrotrophs. There has also been found that mycorrhizal plants are protected both locally and systemically and their protection is related with jasmonic acid levels at their tissues. One of the most important mechanisms for MIR is the so called "priming" that allows plants to exert a fast and efficient defence response. Possible mechanisms to unravel mycorrhizal plants lower defence systems include: defence suppressor activation, differential plants response towards AMF from inexistent to low, and plant defence response suppression during the AMF symbiosis. The symbiosis control is known to be regulated by the plant, however, no role has been assigned to the AMF for the weakening of the plant defence system. Recently, a big step towards understanding of the fungal role has been made. A protein SP7 that interacts with a PR transcription factor ERF19, in the plant nucleus, has been described. This discovery indicates a possible mechanism to establish and maintain the biotrophic status of the AMF counteracting the immune plant system. The main focus of this manuscript is to review the mycorrhizal plant defence responses taking into account that for a functional AMF symbiosis a lesser plant defence mechanism is required. At the same time, the mycorrhizal plant acquires a higher defence capacity against a wide group of attackers.

Keywords : arbuscular mycorrhizal fungi (AMF); plant defense mechanisms; symbiosis; priming; plant protection.

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