Transcriptome Analysis Identifies Key Genes Responsible for Red Coleoptiles in Triticum Monococcum.

Red coleoptiles can help crops to cope with adversity and the key genes that are responsible for this trait have previously been isolated from Triticum aestivum, Triticum urartu, and Aegilops tauschii. This report describes the use of transcriptome analysis to determine the candidate gene that controls the trait for white coleoptiles in T. monococcum by screening three cultivars with white coleoptiles and two with red coleoptiles. Fifteen structural genes and two transcription factors that are involved in anthocyanin biosynthesis were identified from the assembled UniGene database through BLAST analysis and their transcript levels were then compared in white and red coleoptiles. The majority of the structural genes reflected lower transcript levels in the white than in the red coleoptiles, which implied that transcription factors related to anthocyanin biosynthesis could be candidate genes. The transcript levels of MYC transcription factor TmMYC-A1 were not significantly different between the white and red coleoptiles and all of the TmMYC-A1s contained complete functional domains. The deduced amino acid sequence of the MYB transcription factor TmMYB-A1 in red coleoptiles was homologous to TuMYB-A1, TaMYB-A1, TaMYB-B1, and TaMYB-D1, which control coleoptile color in corresponding species and contained the complete R2R3 MYB domain and the transactivation domain. TmMYB-a1 lost its two functional domains in white coleoptiles due to a single nucleotide deletion that caused premature termination at 13 bp after the initiation codon. Therefore, TmMYB-A1 is likely to be the candidate gene for the control of the red coleoptile trait, and its loss-of-function mutation leads to the white phenotype in T. monococcum.

The arbuscular mycorrhizal fungus Rhizophagus irregularis MUCL 43194 induces the gene expression of citrate synthase in the tricarboxylic acid cycle of the phosphate-solubilizing bacterium Rahnella aquatilis HX2.

An increasing number of studies have demonstrated that arbuscular mycorrhizal fungi can cooperate with other soil microorganisms, e.g., bacteria, which develop near or on the surface of the extraradical hyphae where they perform multiple functions. However, the mechanisms involved in this privileged relationship are still poorly known. In the present study, we investigated how the arbuscular mycorrhizal fungus Rhizophagus irregularis MUCL 43194 influences the three pace-making enzymes (i.e., citrate synthase, isocitrate dehydrogenase, and α-oxoglutarate dehydrogenase) of the tricarboxylic acid (TCA) cycle in the phosphate-solubilizing bacterium Rahnella aquatilis HX2. The study was conducted under strict in vitro culture conditions and analysis made at the transcriptional level. Results showed that R. irregularis induced the expression of the gene-encoding citrate synthase (gltA), the pace-making enzyme involved in the first step of the TCA cycle, in R. aquatilis at all time points of observation (i.e., 1, 6, 12, 24, 48, and 72 h). The expression of the gene-encoding isocitrate dehydrogenase (icd) significantly decreased at 6, 12, 24, 48, and 72 h and the expression of the gene-encoding α-oxoglutarate dehydrogenase E1 component (kgdhc) significantly increased at 1, 6, and 48 h. The above results suggested that R. irregularis may influence the level of adenosine triphosphate production in R. aquatilis and thus the metabolism of the bacterium by stimulating the expression of gltA involved in the TCA cycle. Our results suggest a fine-tuned dialog between R. irregularis MUCL 43194 and R. aquatilis HX2 and emphasize the complexity of the interactions that might take place at the hyphal surface of arbuscular mycorrhizal fungi hosting communities of microbes.

Arbuscular mycorrhizal fungi stimulate organic phosphate mobilization associated with changing bacterial community structure under field conditions.

The extraradical hyphae of arbuscular mycorrhizal fungi (AMF) harbour and interact with a microbial community performing multiple functions. However, how the AMF-microbiome interaction influences the phosphorus (P) acquisition efficiency of the mycorrhizal pathway is unclear. Here we investigated whether AMF and their hyphal microbiome play a role in promoting organic phosphorus (P) mineralizing under field conditions. We developed an AMF hyphae in-growth core system for the field using PVC tubes sealed with membrane with different size of pores (30 or 0.45 µm) to allow or deny AMF hyphae access to a patch of organic P in root-free soil. AMF and their hyphae associated microbiome played a role in enhancing soil organic P mineralization in situ in the field, which was shown to be a function of the change in bacteria community on the hyphae surface. The bacterial communities attached to the AMF hyphae surface were significantly different from those in the bulk soil. Importantly, AMF hyphae recruited bacteria that produced alkaline phosphatase and provided a function that was absent from the hyphae. These results demonstrate the importance of understanding trophic interactions to be able to gain insight into the functional controls of nutrient cycles in the rhizosphere.