The cis‐acting CTTC–P1BS module is indicative for gene function of LjVTI12, a Qb‐SNARE protein gene that is required for arbuscule formation in Lotus japonicus

Abstract

SUMMARYThe majority of land plants live in symbiosis with arbuscular mycorrhizal fungi from the phylum Glomeromycota. This symbiosis improves acquisition of phosphorus (P) by the host plant in exchange for carbohydrates, especially under low-P availability. The symbiosome, constituted by root cortex cells accommodating arbuscular mycorrhizal fungal hyphae, is the site at which bi-directional exchange of nutrients and metabolites takes place. Uptake of orthophosphate (Pi) in the symbiosome is facilitated by mycorrhizaspecific plant Pi transporters. Modifications of the potato Pi transporter 3 (StPT3) promoter were analysed in transgenic mycorrhizal roots, and it was found that the CTTC cis-regulatory element is necessary and sufficient for a transcriptional response to fungal colonization under low-Pi conditions. Phylogenetic footprinting also revealed binary combination of the CTTC element with the Pi starvation response-associated PHR1-binding site (P1BS) in the promoters of several mycorrhiza-specific Pi transporter genes. Scanning of the Lotus japonicus genome for gene promoters containing both cis-regulatory elements revealed a strong over-representation of genes involved in transport processes. One of these, LjVTI12, encoding a member of the SNARE family of proteins involved in membrane transport, exhibited enhanced transcript levels in Lotus roots colonized with the arbuscular mycorrhizal fungus Glomus intraradices. Down-regulation of LjVTI12 by RNA interference resulted in a mycorrhiza-specific phenotype characterized by distorted arbuscule morphology. The results highlight cooperative cis-regulation which integrates mycorrhiza and Pi starvation signaling with vesicle trafficking in symbiosome development.

Phosphate Treatment Strongly Inhibits New Arbuscule Development But Not the Maintenance of Arbuscule in Mycorrhizal Rice Roots

“…These data are in accordance with the "birdsfoot" arbuscules described by Gutjahr and Parniske (2013) Feddermann et al, 2010), RAM2 (Wang et al, 2012), VAMP72s (Ivanov et al, 2012), SYP132A (Pan et al, 2016), EXO70I (Zhang et al, 2015), VTI12 (Lota et al, 2013), ERF1 (Devers et al, 2013), RED (Groth et al, 2013;Gutjahr and Parniske, 2013), RAM1/ATA (Rich et al, 2015), RAD1 (Park et al, 2015;Xue et al, 2015), and FatM (Bravo et al, 2016). Hence, P inhibition may be related to the functions of these genes.…”

Network of GRAS Transcription Factors Involved in the Control of Arbuscule Development inLotus japonicus

“…S1). Mycorrhization and AM marker gene expression are generally suppressed under high-Pi conditions, which was recently suggested to be mediated by GA 3 signaling and low levels of DELLA proteins (Nagy et al, 2009;Breuillin et al, 2010;Chen et al, 2011;Floss et al, 2013;Lota et al, 2013). Consistently, the expression of all eight tested mycorrhiza upregulated transcription factors was repressed after a 2-week high-Pi treatment (Supplemental Fig.…”

“…Only a few cis-regulatory elements were reported to be essential for AM-specific gene expression in arbuscule-containing cells, whereas little is known about components of the corresponding transcriptional machinery (Chen et al, 2011;Lota et al, 2013;Xie et al, 2013). Overall, we found 45 transcriptional regulators that were significantly induced during mycorrhiza formation and the expression of which was under the control of Pi ( Fig.…”

“…Loss-of-function mutants and RNAi lines of MtPT4, OsPT11, and maize pht1;6 mutant led to reduced root colonization with premature degeneration of the arbuscules. In addition, RNAi knockdown of VESICLE ASSOCIATED MEMBRANE PROTEIN72 in M. truncatula or SOLUBLE N-ETHYLMALEIMIDE-SENSITIVE FAC-TOR ATTACHMENT PROTEIN RECEPTOR family member L. japonicus VESICLE TRANSPORT THROUGH T-SNARE INTERACTION12 in L. japonicus led to distorted arbuscular development, which provided evidence for a role of these proteins in vesicle trafficking during arbuscule formation (Ivanov et al, 2012;Lota et al, 2013). Moreover, two L. japonicus mutants were reported to be affected in distinct steps of arbuscule development but not during RLS (Groth et al, 2013).…”

The plasma membrane proteome of Medicago truncatula roots as modified by arbuscular mycorrhizal symbiosis

“…Because of the expansion of the host PM around fungal structures, together with metabolite transfer between the two symbionts, PM protein composition is expected to dynamically change during the root colonization process . Current knowledge regarding plant PM protein remodeling events in mycorrhizal plants, however, mainly deals with the involvement of membrane trafficking proteins mediating exocytotic fusion of vesicles with the PM Ivanov et al 2012;Lota et al 2013;Zhang et al 2015;Harrison and Ivanov 2017) and the transcriptional regulation of plant genes encoding PM nutrient transporters (reviewed by Garcia et al 2016).…”