A transcriptome analysis of a citrus rootstock Poncirus trifoliata identified genes associated with arbuscular mycorrhizal symbiosis
To date, little is known about molecular mechanisms by which woody plants engage symbiosis with arbuscular mycorrhizal (AM) fungi. Here we investigated transcriptome changes in the roots of Poncirus trifoliata (the most common citrus rootstock) that are induced during colonization of an AM fungus Glomus versiforme (Gv). A total of 282 Poncirus genes were differentially expressed in response to Gv colonization, of which 138 could identify homologous genes from the model legume Medicago truncatula that also exhibit similar AM-induced transcriptional changes, while the remaining 144 do not. A high proportion of the AM-responsive Poncirus genes are predicted to be involved in transcription regulation, transport process, cellular organization and protein degradation, implicating these processes in the establishment of AM symbiosis. Promoter-GUS analysis of six AM-induced Poncirus genes [encoding an exocyst subunit (PtrEXO70I), two transcription factors (PtNAC1 and PtPALM1), one chitinase (PtrChit2), one plastid movement associated protein (PtrPMI2) and one lipase (PtrLipase3)] showed that all of them exhibit specific expression in arbuscule-containing root cortical cells, suggesting their potential involvement in establishing AM symbiosis. Notably, down-regulation of the ortholog of PtrExo70I in Medicago by RNAi significantly impaired arbuscule development, indicating that Exo70I is an important host component required for arbuscule development in root cortical cells. This study not only helps identify conserved host genes engaged in AM symbiosis but should also guide future mechanistic studies of potentially Poncirus-specific events during its symbiosis with AM fungi. Overall design: Six samples, the Poncirus trifoliata (L.) Raf roots inoculated by Glomus versiforme (Gv) or roots from uninoculated control were subjected to RNA-seq analysis with three biological replicates, respectively.
External Link: /pubmed:30312435