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Paszkowski Group: Root type contribution to phosphate nutrition of rice during asymbiosis and interaction with symbiotic fungi

GFC / OTHER

Supervisor: Uta Paszkowski (Plant Sciences

PhD projects #1 and #2 'Cereal Symbiosis'

Phosphate (Pi) is an essential plant macronutrient and occurs in scarce amounts in most soils, which frequently limits plant growth. Plant fitness and crop productivity is directly influenced by the plant root system's efficiency in exploring soil nutrient resources. Plant root systems are composed of distinct root types (RTs), and their ratio and spatial arrangement define root system architecture and nutrient foraging properties. RTs may individually respond to their abiotic and biotic soil microenvironment, thereby asymmetrically contributing to plant nutrient acquisition. Surprisingly however, RTs are 'under-investigated' in particular in adult crops where RT-focused research is missing. The Cereal Symbiosis group has addressed this gap in knowledge by studying the RTs of adult rice plants. The root system of adult rice is composed of three RTs, the crown, large and fine lateral roots (CR, LLR, FLR, respectively) with distinct developmental and anatomical characteristics (1). Plants acquire Pi either directly or in association with naturally prevalent arbuscular mycorrhizal (AM) fungi. In rice, the different RTs exhibit variable extent of colonization with LLR fully and CR partially colonized, whereas FLRs remain non-colonized. Exposing rice roots to a beneficial AM fungus leads to the profound modulation of each RT transcriptome, indicative of a switch in their functional relationship (2).

PhD Project #1:

The contribution of individual RTs to rice Pi nutrition in asymbiosis or during interaction with AM fungi remains at present unclear and represents the main objective of this PhD project. The application of interdisciplinary techniques including analytics, imaging and molecular genetics will deliver an insight into in situ phosphorus fluxes at unprecedented spatio-temporal resolution. The study will inform about RT functioning, important for rational breeding approaches towards improved plant stress tolerance and crop productivity.

PhD Project #2:

CRs can reach a diameter of >1mm, LLRs of ~370µm and FLRs of ~160µm and contribute to varying extend to the uptake of phosphate. Furthermore, CRs and LLRs engage with phosphate delivering arbuscular mycorrhizal fungi whereas FLRs do not. The project seeks to develop a mathematical model to represent and quantify the fluxes of phosphate across the three RTs in the presence and absence of the beneficial fungus. The student will be co-supervised by Dr. Uta Paszkowski (biological part) and Prof. Tiina Roose, University Southampton (mathematical part).

1. Gutjahr C, Casieri L, & Paszkowski U (2009) Glomus intraradices induces changes in root system architecture of rice independently of common symbiosis signaling. New Phytol 182(4):829-837.
2. Gutjahr C, et al. (2 015) Transcriptome diversity among rice root types during asymbiosis and interaction with arbuscular mycorrhizal fungi. Proc Natl Acad Sci U S A 112(21):6754-6759.

PhD project #3: 'Cereal Symbiosis'

Sweet talk in arbuscular mycorrrhizal symbiosis of rice

Arbuscular mycorrhizal (AM)c symbioses profoundly influence plant, including crop nutrition and thereby productivity. Furthermore, it represents one of the most ubiquitous and ancient symbioses on the planet that allows intimate interplay between roots of terrestrial plant species and fungi of the Glomeromycotina. The resulting interaction is mutually beneficial due to the exchange of plant-derived organic carbon for fungus-delivered soil nutrients. Establishment of AM symbiosis depends on mutual plant-fungal recognition involving the release of diffusible signals into the rhizosphere. The Cereal Symbiosis group recently discovered the first plant N-acetylglucosamine (GlcNAc) transporter encoded by NOPE1 (NO PErception 1) and showed that it is critical in pre-symbiotic signalling [Nadal M, Sawers R, et al. Nature Plants (2017) 3, 17073]. Root exudates of nope1 plants fail to induce diagnostic transcriptional responses in the fungus, suggesting a requirement for NOPE1 in conditioning the fungus for symbiosis. This PhD project builds on this landmark discovery and aims to elucidate the mechanisms underpinning NOPE1-dependent communication in AM symbiosis.

We have recently observed that during symbiosis, both rice and fungus simultaneously induce homologous GlcNAc transporter genes, OsNOPE1 and RiNGT1 respectively. An intriguing possibility is thus that plant and fungus 'communicate' during the physical association via the exchange of signals using the same type of transporter protein. The PhD project will apply molecular cell biology approaches to determine the spatial coordination of plant and fungal GlcNAc transporters.