Bacteria as a growth supplement for plants

What factors are vitally important for plant growth? 

Soil composition, mineral nutrients, sunlight, water, oxygen, and carbon dioxide are well-established answers. Bacteria that reside on plant leaves are another crucial factor, a multi-institutional team of researchers argues in a recent study. 

Bacteria that live in plant roots have previously been demonstrated to influence the growth of leaves. Whether and how leaf growth is affected by the bacteria that reside on leaves has been unclear, however. 

Researchers used Zea mays (maize) to investigate this question. They constructed a synthetic community of 210 bacterial strains and applied them to maize leaves. More growth was observed for the youngest leaves treated with the bacteria, compared to those untreated. In order to understand why, the team sequenced the maize RNA to determine how gene expression in leaves changed in response to the microbiota. Decreased expression of defense genes and increased expression of growth genes was observed only in the youngest, bacteria-treated leaves. Moreover, they found that the young, bacteria-treated leaves were most susceptible to a common maize-infecting fungus, Fusarium graminearum, supporting the hypothesis that leaf microbiota repress immune defense and promote growth in leaves.

This study raises numerous fascinating questions, such as how exactly bacteria are physically or chemically stimulating growth, what pathways are controlling the shift from defense to growth in the leaf cells, whether there is any promise for improved plant growth with the use of plant-targeting immunosuppressants, and to what extent there is synergism between leaf microbiota and root microbiota in the defense-growth effect.

Study credit: This study was led by Valéria Custódio and others at University of Nottingham, along with collaborators at Universidad Nacional Autónoma de México.

Managing Correspondent: Wilaysha Evans

Research article: https://www.cell.com/action/showPdf?pii=S1931-3128%2825%2900030-7 (Cell Host & Microbe)

Press release article: https://www.the-microbiologist.com/news/genetic-switch-controlling-microbiota-impact-could-help-control-leaf-growth-in-poor-soils/5276.article (The Microbiologist)

Image credit: GettyImages/enviromantic