Attracting useful bacteria
Plants that grow in challenging environments, like limited nutrients, often attract microbes that can help them. Maybe one of the most well-known examples is the attraction of nitrogen fixing bacteria by legumes.
But there are lots of other microbes who with the correct encouragements can help plants. Not surprisingly, researchers are looking at which through the plant exuded substances attract useful microbes, which microbes specifically, and what they do.
One of the microbe attracting substances is apigenin. This substance is among others attracting the nitrogen fixing bacteria Azospirillum brasilense. These bacteria, in contrast to the more known rhizobia bacteria, are not involved in a close symbiotic relationship with the plant. It forms a biofilm, a thin layer around the root to create the oxygen deficient environment needed for nitrogen fixation. This does, however, enables easy access to the through nitrogen fixation freed nitrogen.
Extra apigenin in wheat
But the question is can plants, and crops in particular, be adapted in such a way that they attract more of these bacteria. A group of American researchers show in an article named “Increased Apigenin in DNA-Edited Hexaploid Wheat Promoted Soil Bacterial Nitrogen Fixation and Improved Grain Yield Under Limiting Nitrogen Fertiliser” that it is possible.
In wheat aspigenin is an intermediate product in the production of flavonoids. From the enzyme named CYP75B it is known that in rice it is transferring apigenin to luteolin. The researchers looked if this enzyme is also present in wheat. They found that wheat has eleven look-a-likes. Nine of these genes produce a complete enzyme. These nine the researchers placed in yeast to find out if the enzymes were working as expected. This turned out to be the case for seven of them.
Subsequently the researchers deactivated all nine on CYP75B like genes. That worked only partial. But when the researchers looked at the amount of apigenin in those plants, they noticed that it was enough. Plants which had some CYP75B deactivated contained more apigenin. Also, their roots exuded more apigenin.
A clear effect
Subsequently the researchers studied the effect of the increased apigenin exudation on the bacterium Azospirillum brasilense. The researchers gave Azospirillum brasilense fluorescent labels, one for detection and one for biofilm formation. In this way the researchers observed that the exuded apigenin attracted more Azospirillum brasilense. The bacterium van not just present on the roots but also created that thin oxygen excluding layer.
Lastly the researchers studied the effect of this on wheat growth and yield. Under circumstances with enough nitrogen plants without and with extra apigenin exudate did just as well. However, at the moment when less nitrogen was available, plants with extra apigenin did better. Not only did the grew bigger and produced more grains, but those grains also contained just as much nitrogen as grains produced under circumstances with enough nitrogen. Something the control plants in nitrogen poor circumstances did not do.
Apigenin is thus helping to attract nitrogen fixing bacteria that are also active. Through breeding of crops that produce more apigenin it would be possible to use less fertilization.
Literature
Tajima, H., A. Yadav, J. H. Castellanos, et al. 2025. “Increased Apigenin in DNA-Edited Hexaploid Wheat Promoted Soil Bacterial Nitrogen Fixation and Improved Grain Yield Under Limiting Nitrogen Fertiliser.” Plant Biotechnology Journal 1–15. https://doi.org/10.1111/pbi.70289.
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