The biological significance of genetic variation in arbuscular mycorrhizal colonisation in rice

Abstract

A variety of crops, including different types of rice, are colonised by arbuscular mycorrhizal fungi (AMF), which possess the ability to effectively absorb essential nutrients, such as phosphate, from the surrounding soil. The utilisation of mycorrhizal symbioses in agricultural systems is a highly promising strategy for the development of resource-efficient and ecologically sustainable agricultural practises. AMF colonisation with rice tends to be low under flooding regimes due to the domination by anaerobic processes. However, understanding rice-AMF interaction under non-flooded conditions is of key importance for improving nutrient and water use efficiency. AMF colonisation by Rhizophagus irregularis in rice showed a wide range of genetic diversity. This work seeks to determine the biological significance of that variation. Five cultivars were selected because of consistent differences in colonisation. By using three pots with different mesh exclusion systems, AMF (R. irregularis) and rice roots were orientated to the supply of phosphate, where calcium hydrogen phosphate (CaHPO4) was either inaccessible (solid barrier “control”), accessible only to the AMF (20 μm mesh) or accessible to both the AMF and rice roots (2 mm mesh). We found significant differences in plant heights, tillers, biomass, and AMF colonisation across all our pot systems. There was a big genetic difference in AMF colonisation. AMF colonisation was limited in 2 mm mesh compared to control and 20 µm mesh. A massive increase of P uptake in 20 μm mesh demonstrates AMF-driven P acquisition. However, naturally inoculated (Soil) experiments revealed lower percentage of AMF colonisation than those with sand inoculated with R. irregularis. The differences in colonisation observed in experiments with R. irregularis are not observed in soils containing a diverse inoculum of AMF species. The transcriptomic data of the rice roots reveals that the expression of AM marker genes especially OsPT11 was significantly expressed in comparison with 2 mm mesh and control. This indicates that some of P were delivered to the rice plant through AMF symbiosis. Transcriptome analysis of contrasting genotypes and mesh treatments reveals a new understanding of AMF and P transporter and starvation genes, which provides important sources for the field of rice and AMF.