The potential role of Mucoromycotina 'fine root endophytes' in plant nitrogen nutrition.

Mycorrhizal associations between fungi and plant roots have globally significant impacts on nutrient cycling. Mucoromycotina 'fine root endophytes' (MFRE) are a distinct and recently characterised group of mycorrhiza-forming fungi that associate with the roots of a range of host plant species. Given their previous misidentification and assignment as arbuscular mycorrhizal fungi (AMF) of the Glomeromycotina, it is now important to untangle the specific form and function of MFRE symbioses. In particular, relatively little is known about the nature of MFRE colonisation and its role in N uptake and transfer to host plants. Even less is known about the mechanisms by which MFRE access and assimilate N, and how this N is processed and subsequently exchanged with host plants for photosynthates. Here, we summarise and contrast the structures formed by MFRE and arbuscular mycorrhizal fungi in host plants as well as compare the N source preference of each mycorrhizal fungal group with what is currently known for MFRE N uptake. We compare the mechanisms of N assimilation and transfer to host plants utilised by the main groups of mycorrhizal fungi and hypothesise potential mechanisms for MFRE N assimilation and transfer, outlining directions for future research.

Genetic Screening for Mutants with Altered Seminal Root Numbers in Hexaploid Wheat Using a High-Throughput Root Phenotyping Platform.

Roots are the main channel for water and nutrient uptake in plants. Optimization of root architecture provides a viable strategy to improve nutrient and water uptake efficiency and maintain crop productivity under water-limiting and nutrient-poor conditions. We know little, however, about the genetic control of root development in wheat, a crop supplying 20% of global calorie and protein intake. To improve our understanding of the genetic control of seminal root development in wheat, we conducted a high-throughput screen for variation in seminal root number using an exome-sequenced mutant population derived from the hexaploid wheat cultivar Cadenza. The screen identified seven independent mutants with homozygous and stably altered seminal root number phenotypes. One mutant, Cadenza0900, displays a recessive extra seminal root number phenotype, while six mutants (Cadenza0062, Cadenza0369, Cadenza0393, Cadenza0465, Cadenza0818 and Cadenza1273) show lower seminal root number phenotypes most likely originating from defects in the formation and activation of seminal root primordia. Segregation analysis in F2 populations suggest that the phenotype of Cadenza0900 is controlled by multiple loci whereas the Cadenza0062 phenotype fits a 3:1 mutant:wild-type segregation ratio characteristic of dominant single gene action. This work highlights the potential to use the sequenced wheat mutant population as a forward genetic resource to uncover novel variation in agronomic traits, such as seminal root architecture.