Symbioses of bacteria with fungi have only recently been described and are poorly understood. In the symbiosis of Mycetohabitans (formerly Burkholderia) rhizoxinica with the fungus Rhizopus microsporus, bacterial type III (T3) secretion is known to be essential. Proteins resembling T3-secreted transcription activator-like (TAL) effectors of plant pathogenic bacteria are encoded in the three sequenced Mycetohabitans spp. genomes. TAL effectors nuclear-localize in plants, where they bind and activate genes important in disease. The Burkholderia TAL-like (Btl) proteins bind DNA but lack the N- and C-terminal regions, in which TAL effectors harbor their T3 and nuclear localization signals, and activation domain. We characterized a Btl protein, Btl19-13, and found that, despite the structural differences, it can be T3-secreted and can nuclear-localize. A btl19-13 gene knockout did not prevent the bacterium from infecting the fungus, but the fungus became less tolerant to cell membrane stress. Btl19-13 did not alter transcription in a plant-based reporter assay, but 15 R. microsporus genes were differentially expressed in comparisons both of the fungus infected with the wild-type bacterium vs. the mutant and with the mutant vs. a complemented strain. Southern blotting revealed btl genes in 14 diverse Mycetohabitans isolates. However, banding patterns and available sequences suggest variation, and the btl19-13 phenotype could not be rescued by a btl gene from a different strain. Our findings support the conclusion that Btl proteins are effectors that act on host DNA and play important but varied or possibly host genotype-specific roles in the M. rhizoxinica–R. microsporus symbiosis.

细菌与真菌的共生体只是最近才被描述，人们对此知之甚少。在的共生Mycetohabitans（以前伯克霍尔德）rhizoxinica用真菌根霉microsporus，细菌型III（T3）的分泌已知是必要的。在三种测序的Mycetohabitans中编码类似于植物病原细菌的T3分泌转录激活因子（TAL）效应子的蛋白质spp。基因组。TAL效应子在植物中发生核定位，它们结合并激活对疾病重要的基因。伯克霍尔德菌TAL样（Btl）蛋白与DNA结合，但缺少N和C端区域，其中TAL效应子带有T3和核定位信号以及激活域。我们对Btl蛋白Btl19-13进行了表征，发现尽管存在结构差异，但它可以T3分泌并可以进行核定位。一个btl19 -13基因敲除并未阻止细菌感染的真菌，而真菌变得宽容细胞膜压力越少。Btl19-13不会改变基于植物的报告基因检测中的转录，但是会改变15个小孢子虫在用野生型细​​菌与突变体感染的真菌和与突变体与互补菌株感染的真菌的比较中，基因差异表达。Southern印迹透露BTL在14层多元的基因Mycetohabitans分离。然而，条带图案和可用的序列表明变化和btl19-13表型不能由一个被营救BTL从不同菌株的基因。我们的发现支持这样的结论，即Btl蛋白是作用于宿主DNA的效应子，并在根际分枝杆菌– R. microsporus共生中发挥重要但多样或可能不同的宿主基因型特异性作用。