Gibberellin (GA) phytohormones are ubiquitous regulators of growth and developmental processes in vascular plants. The convergent evolution of GA production by plant-associated bacteria, including both symbiotic nitrogen-fixing rhizobia and phytopathogens, suggests that manipulation of GA signaling is a powerful mechanism for microbes to gain an advantage in these interactions. Although orthologous operons encode GA biosynthetic enzymes in both rhizobia and phytopathogens, notable genetic heterogeneity and scattered operon distribution in these lineages, including loss of the gene for the final biosynthetic step in most rhizobia, suggest varied functions for GA in these distinct plant-microbe interactions. Therefore, deciphering GA operon evolutionary history should provide crucial evidence toward understanding the distinct biological roles for bacterial GA production. To further establish the genetic composition of the GA operon, two operon-associated genes that exhibit limited distribution among rhizobia were biochemically characterized, verifying their roles in GA biosynthesis. This enabled employment of a maximum parsimony ancestral gene block reconstruction algorithm to characterize loss, gain, and horizontal gene transfer (HGT) of GA operon genes within alphaproteobacterial rhizobia, which exhibit the most heterogeneity among the bacteria containing this biosynthetic gene cluster. Collectively, this evolutionary analysis reveals a complex history for HGT of the entire GA operon, as well as the individual genes therein, and ultimately provides a basis for linking genetic content to bacterial GA functions in diverse plant-microbe interactions, including insight into the subtleties of the coevolving molecular interactions between rhizobia and their leguminous host plants.

中文翻译：

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解开缠结的绞线：细菌赤霉素生物合成操纵子的进化分析。

赤霉素 (GA) 植物激素是维管植物中普遍存在的生长和发育过程的调节剂。植物相关细菌（包括共生固氮根瘤菌和植物病原体）产生 GA 的趋同进化表明，操纵 GA 信号是微生物在这些相互作用中获得优势的强大机制。尽管直系同源操纵子在根瘤菌和植物病原体中编码 GA 生物合成酶，但这些谱系中显着的遗传异质性和分散的操纵子分布，包括大多数根瘤菌中最后生物合成步骤的基因丢失，表明 GA 在这些不同的植物 - 微生物相互作用中具有不同的功能. 所以，破译 GA 操纵子的进化历史应该为理解细菌 GA 产生的不同生物学作用提供重要的证据。为了进一步确定 GA 操纵子的遗传组成，对两个在根瘤菌中分布有限的操纵子相关基因进行了生化表征，验证了它们在 GA 生物合成中的作用。这使得能够使用最大简约祖先基因块重建算法来表征 alphaproteobacterial 根瘤菌中 GA 操纵子基因的丢失、增益和水平基因转移 (HGT)，这些基因在包含这种生物合成基因簇的细菌中表现出最大的异质性。总的来说，这种进化分析揭示了整个 GA 操纵子的 HGT 以及其中的单个基因的复杂历史，