Insights into the complex role of GRAS transcription factors in the arbuscular mycorrhiza symbiosis

authored by: Rico M. Hartmann, Sieke Schaepe, Daniel Nübel, Arne C. Petersen, Martina Bertolini, Jana Vasilev, Helge Kuester, Natalija Hohnjec
Abstract: To improve access to limiting nutrients, the vast majority of land plants forms arbuscular mycorrhizal (AM) symbioses with Glomeromycota fungi. We show here that AM-related GRAS transcription factors from different subgroups are upregulated during a time course of mycorrhization. Based on expression studies in mutants defective in arbuscule branching (ram1-1, with a deleted MtRam1 GRAS transcription factor gene) or in the formation of functional arbuscules (pt4-2, mutated in the phosphate transporter gene MtPt4), we demonstrate that the five AM-related GRAS transcription factor genes MtGras1, MtGras4, MtGras6, MtGras7, and MtRad1 can be differentiated by their dependency on MtRAM1 and MtPT4, indicating that the network of AM-related GRAS transcription factors consists of at least two regulatory modules. One module involves the MtRAM1- and MtPT4-independent transcription factor MtGRAS4 that activates MtGras7. Another module is controlled by the MtRAM1- and MtPT4-dependent transcription factor MtGRAS1. Genome-wide expression profiles of mycorrhized MtGras1 knockdown and ram1-1 roots differ substantially, indicating different targets. Although an MtGras1 knockdown reduces transcription of AM-related GRAS transcription factor genes including MtRam1 and MtGras7, MtGras1 overexpression alone is not sufficient to activate MtGras genes. MtGras1 knockdown roots display normal fungal colonization, with a trend towards the formation of smaller arbuscules.
Organisation(s): Institute of Plant Genetics
External Organisation(s): Universita Degli Studi di Milano-Bicocca
Type: Article
Journal: Scientific reports
Volume: 9
ISSN: 2045-2322
Publication date: 2019
Publication status: Published
Peer reviewed: Yes
ASJC Scopus subject areas: General
Electronic version(s): https://doi.org/10.1038/s41598-019-40214-4 (Access: Open)
https://doi.org/10.15488/4843 (Access: Open)