Secreted TAL effectors protect symbiotic bacteria from entrapment within fungal hyphae

Abstract

The association of the agriculturally significant phytopathogenic fungus Rhizopus microsporus with the bacterial endosymbiont Burkholderia rhizoxinica is a remarkable example of bacteria controlling host physiology and reproduction. Here, we show that a group of transcription activator-like effectors (TALEs) called Burkholderia TALE-like proteins (BATs) from B. rhizoxinica are essential for the establishment of the symbiosis. Mutants lacking BAT proteins are unable to induce host sporulation. Utilising novel microfluidic devices in combination with fluorescence microscopy we observed the accumulation of BAT-deficient mutants in specific fungal side-hyphae with accompanying increased fungal re-infection. High-resolution live imaging revealed septa biogenesis at the base of infected hyphae leading to compartmental trapping of BATdeficient endobacteria. Trapped endosymbionts showed reduced intracellular survival, suggesting a protective response from the fungal host against bacteria lacking specific effectors. These findings underscore the involvement of BAT proteins in maintaining a balance between mutualism and antagonism in bacterial-fungal interactions and provide deeper insights into the dynamic interactions between bacteria and eukaryotes.Bacteria living in close association with eukaryotic hosts may control and exploit their host via pathogenic or mutualistic interactions 1 . For

Let’s Get Physical: Bacterial-Fungal Interactions and Their Consequences in Agriculture and Health

“…Holrhizin A exhibited biosurfactant activity, altered biofilm formation and cell motility to promote colonization [ 25 ]. Work pioneered by several research groups has discovered the involvement of effectors-Type III secretion system (T3SS) [ 26 ], transcription activator-like (TAL) effector [ 27 , 28 ], and Type II secretion system (T2SS) [ 23 ]. Receptors that interact with these effectors and the downstream signaling pathways eliciting specific responses remain to be identified.…”

“…In the interaction between Rhizopus microsporus and Mycetohabitans rhizoxinica , fungal sporulation is contingent upon the successful establishment of symbiosis, which ensures maintenance of mutualism over generations [ 50 ]. Establishment of endofungal symbiosis between CaGg and G. margarita results in increased fungal sporulation [ 27 ]. In both cases, endobacteria are found in the spores, suggesting that control of host sporulation by endobacteria is sufficient to regulate their own transmission.…”

“…The bacterial dinitrogen reductase required to convert atmospheric dinitrogen gas into ammonia was transcribed by the fungus under adequate N. Co-inoculation of rice plants with both partners was shown to promote plant growth and plant nitrogen nutrition [ 95 ]. Interaction between CaGg and G. margarita promotes fungal response to strigalactones, which are plant small molecules that stimulate branching and establishment of AMF symbioses [ 27 ]. MHB are mycorrhizal helper bacteria defined as bacteria that positively interact with established symbiosis between mycorrhizal fungi and plants, or mycorrhization helper bacteria that facilitate symbiosis between mycorrhizal fungi and plants [ 46 ].…”

Gene editing tools and the treatment of cystic fibrosis disease

“…Components of this method include the transcription activator-like effector (TALE) DNA binding domain and DNA cleavage domain (FokI) (Barnett 2018) (Figure 2). TALEs are proteins secreted by the bacteria and help them to bind to sequences in the plant host genome (Richter, et al 2020). The DNA binder domain has repeated 33-35 amino acid sequences, in which the 12th and 13th amino acids are called the Repeat Variable Diresidue (RVD), are highly variable, and able to recognize a nucleotide (Malzahn and Qi 2021).…”

“…They compared different transfection methods (lipofectamine versus electroporation) and formats (plasmid DNA versus ribonucleoprotein) in delivering the CRISPR/Cas9 elements along with single-stranded oligodeoxynucleotides (ssODNs) to clinically relevant cells targeting major CFTR mutation loci. Their findings showed that among different combinations, electroporation of CRISPR/Cas9 and guide RNA (gRNA) ribonucleoprotein (Cas9 RNP) is the most effective strategy, leading to achieving a greater than 20% precise correction rate when it is applied to a patient-derived iPSC line carrying the dF508 mutation (Ruan, et al 2019). On the other hand, Smirnikhina et al (2020) tested P.F508del editing in cells from cystic fibrosis patients.…”