Transcriptional and post-translational control of arbuscular mycorrhiza development in Lotus japonicus

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In this project the interaction profiles of GRAS protein RAM1 and DNA-binding AP2 transcription factor (TF) CBX1 serve as a framework for investigating the distinct and cooperative activities of GRAS and AP2 proteins in the arbuscular mycorrhizal symbiosis (AMS). The RAM1-CBX1 DNA-binding multiprotein complex which is presumed to be composed of at least three GRAS transcriptional regulators (TRs) and CBX1 will be investigated in Lotus japonicus. The RAM1-CBX1 complex is thought to be involved in the regulation of processes underlying a functional AMS and serving the reciprocal exchange of essential nutrients at the interface between host plant and AM fungus. The nature of this heterocomplex and the genes which it targets during defined genetic stages of AMS development will be elucidated in conjunction with a series of L. japonicus genotypes associated with single- and multi-genic mutations in loci encoding involved GRAS and AP2 proteins. We aim to (1) identify DNA-binding bona fide TF(s) that cooperate with GRAS proteins during AMS development, (2) uncover novel interaction partners in the RAM1-CBX1 regulatory network(s), a central processing unit of AMS, (3) explore the transcriptional activity of studied TF complex(es), and (4) study the evolutionary conservation of CBX1-RAM1 complex components through complementation of mutant phenotypes in L. japonicus and other land plant species. Overall, this study aims to explore the RAM1-CBX1 transcriptional regulatory network as the central processing unit of AMS, as well as to identify the RAM1-CBX1 target genes involved in the reciprocal exchange of nutrients and other essential AMS processes.Knowing the genetic trait components of AMS will give us the tools to modify developmental, metabolic, transport and growth processes in mycorrhizal plants including crops. A thorough understanding of the AMS regulatory network and underlying regulatory hierarchies, essential target genes and regulated downstream processes may allow reconstruction of AMS in species with poor or intermediate responsiveness to AM fungi or even in non-host species.