Dynamics of roots and AM colonization in rice plants growing in changing environmental conditions.

Arbuscular mycorrhiza (AM) is an association established between 80% of land plants and soil fungi. AM fungi are considered to have played a key role in the origin of land flora, assisting plants in nutrient absorption from soil. However, some plants are immune to AM colonization and the mechanism which control such event is still unknown. Unlike many other host plants, Oryza sativa has a differentiated root system consisting of: crown roots which originate large lateral roots (LLRs) profusely colonized by AM fungi, and fine lateral roots (FLRs) which do not support AM colonization. Morphological observations demonstrate that FLRs lack a layered cortex which seems to be required for arbuscule formation. In addition, the absence of hyphopodia adhering to FLRs suggests that the cross-talk between plant and AM fungi is also impaired. The goal of our work was to investigate the molecular determinants which control the interaction between AM fungi and a plant where host and non-host roots are simultaneously present. To this purpose, LLRs and FLRs were separately collected from mycorrhizal and control plants, and processed for RNA-seq. The transcriptional profiles of each root-type revealed different enriched GO categories (i.e. response to biotic stimuli) which grouped genes potentially acting as regulators of the morphogenesis of root typologies, as well as of their interaction with AM fungi. These results will enhance our understanding of the dynamics involved in the AM establishment, identifying genes which are responsible of the fungal recognition in a complex genetic background, as the rice hostplant.