A biosynthetic gene cluster in rhizobia is responsible for producing gibberellin phytohormones

What is it about?

Plants produce gibberellin (GA) phytohormones to control various aspects of growth and development. However, it has also been shown that plant-associated microbes, both fungal and bacterial, can produce GA as well, presumably as a mechanism to manipulate their plant host. Many rhizobia, which are the nitrogen-fixing symbionts of legumes, contain a conserved biosynthetic gene cluster that has been postulated to be involved in bacterial biosynthesis of GA. In this paper, we describe the functional characterization of five enzymes from this gene cluster, showing that they act consecutively to produce GA. Our results not only describe biosynthesis of GA in bacteria for the first time, but also demonstrate that bacteria have evolved biosynthesis of this plant hormone independently of either plants or fungi.

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Why is it important?

The gibberellin (GA) phytohormones are crucial to the growth and development of vascular plants. Thus, understanding the production and function of GA has implications for our understanding of plant biology more broadly. Also, because plant-associated microbes also produce GA, it is likely that these organisms are attempting to manipulate the plants for their own fitness advantage, potentially at the expense of the plant. In this paper, we investigated the phenomenon of GA biosynthesis in rhizobia, which are crucial for the agricultural importance of legumes, including soybean, which is a major cash crop. Our work towards elucidating GA biosynthesis in these legume symbionts will help to better our undestanding of this crucial symbiosis.