Foreign AT-rich genes drive bacterial adaptation to new niches while challenging the existing regulation network. Here we report that MucR, a conserved regulator in α-proteobacteria, balances adaptation and regulatory integrity in Sinorhizobium fredii, a facultative microsymbiont of legumes. Chromatin immunoprecipitation sequencing coupled with transcriptomic data reveal that average transcription levels of both target and non-target genes, under free-living and symbiotic conditions, increase with their conservation levels. Targets involved in environmental adaptation and symbiosis belong to genus or species core and can be repressed or activated by MucR in a condition-dependent manner, implying regulatory integrations. However, most targets are enriched in strain-specific genes of lower expression levels and higher AT%. Within each conservation levels, targets have higher AT% and average transcription levels than non-target genes and can be further up-regulated in the mucR mutant. This is consistent with higher AT% of spacers between −35 and −10 elements of promoters for target genes, which enhances transcription. The MucR recruitment level linearly increases with AT% and the number of a flexible pattern (with periodic repeats of Ts) of target sequences. Collectively, MucR directly represses AT-rich foreign genes with predisposed high transcription potential while progressive erosions of its target sites facilitate regulatory integrations of foreign genes.

富含 AT 的外来基因驱动细菌适应新的生态位，同时挑战现有的调控网络。在这里，我们报告 MucR 是 α-变形菌中的一种保守调节剂，可平衡Sinorhizobium fredii 的适应性和调节完整性，豆类的兼性微生物共生体。染色质免疫沉淀测序与转录组学数据相结合表明，在自由生活和共生条件下，目标基因和非目标基因的平均转录水平随着它们的保护水平而增加。参与环境适应和共生的目标属于属或种核心，可以被 MucR 以条件依赖的方式抑制或激活，这意味着监管整合。然而，大多数目标都富含表达水平较低和 AT% 较高的菌株特异性基因。在每个保护水平内，目标基因比非目标基因具有更高的 AT% 和平均转录水平，并且可以在mucR中进一步上调变种人。这与目标基因启动子的 -35 和 -10 元件之间的间隔子的 AT% 更高，从而增强转录。MucR 募集水平随 AT% 和目标序列的灵活模式（Ts 的周期性重复）的数量线性增加。总的来说，MucR 直接抑制具有易感高转录潜能的富含 AT 的外来基因，而其靶位点的渐进侵蚀促进了外来基因的调节整合。