The role of GRAS-domain proteins in arbuscular mycorrhizal symbiosis

Luginbuehl, Leonie (2016) The role of GRAS-domain proteins in arbuscular mycorrhizal symbiosis. Doctoral thesis, University of East Anglia.

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Abstract

A major limitation to plant growth is the restricted access to nutrients in the soil. To
improve nutrient acquisition, the majority of land plants enter a beneficial symbiosis
with arbuscular mycorrhizal (AM) fungi. The accommodation of fungal hyphae in roots
requires the extensive transcriptional reprogramming of host cells. Several GRASdomain
proteins, including NSP1 (NODULATION SIGNALLING PATHWAY 1), NSP2, and
RAM1 (REQUIRED FOR ARBUSCULAR MYCORRHIZATION 1), have emerged as
important transcriptional regulators during mycorrhization. Interaction studies suggest
that these proteins form multicomponent complexes, raising the question whether they
regulate similar or different mycorrhizal processes. Here, the functions of NSP1, NSP2
and RAM1 during AM development were investigated by detailed phenotypic and
transcriptional analyses of the corresponding loss‐of‐function mutants.
Global gene expression profiling of nsp1‐1 revealed that NSP1 is required for the
expression of a large number of genes involved in strigolactone and gibberellin
biosynthesis at the pre‐contact stage of AM development. Strigolactones are known to
attract the fungus to the root. In line with this, the quantification of mycorrhizal
structures showed a delay in mycorrhization in nsp1‐1. Transcriptional profiling
confirmed that the expression of the majority of mycorrhizal‐induced genes was
delayed, but not abolished in nsp1‐1, suggesting that NSP1 only has a minor role in the
transcriptional regulation once the contact between the fungus and the roots has been
established. Unlike NSP1, RAM1 plays a critical role in the transcriptional regulation at
later stages of AM symbiosis. Mycorrhization was strongly impaired in ram1‐1, and
transcriptional profiling revealed that RAM1 is essential for the expression of several
genes involved in arbuscule development and the nutrient exchange between the
symbionts. Meanwhile, the exact function of NSP2 remains unclear, as no effect on
mycorrhization was observed in nsp2‐2 under the conditions tested here. These findings
suggest that NSP1, NSP2 and RAM1 play largely different roles in the transcriptional regulation during AM development.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Biological Sciences
Depositing User:	Jackie Webb
Date Deposited:	09 Mar 2017 11:20
Last Modified:	02 May 2019 00:38
URI:	https://ueaeprints.uea.ac.uk/id/eprint/62928
DOI:

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