Scientists Find Single Enzyme Controling Growth and Defense Hormones

In a paper published in the November 14 issue of Proceedings of the National Academy of Sciences, scientists at Washington University in St. Louis report that the enzyme GH3.5 can control the levels of two plant hormones, auxin and salicylic acid. GH3.5 is the first enzyme of its kind known to control completely different classes of hormones.

Auxin controls various plant responses, including cell and tissue growth and development, while salicylic acid helps plants respond to infections, which often affects growth. Plants must carefully control the levels of auxin and salicylic acid to properly grow and react to new threats. To find out how GH3.5 controls multiple hormones, the researchers induced plants to accumulate large amounts of the protein and then measured their levels of hormones. When GH3.5 was expressed at high levels, both auxin and salicylic acid were reduced. Without auxin, the plants stayed small and stunted.

To prove that GH3.5 regulates distinct classes of hormones, the research team crystallized GH3.5. The researchers fired powerful X-rays into the protein crystal, and the diffraction of the X-rays provided information about the atom-by-atom structure of the enzyme. They found that the part of the enzyme that binds and modifies hormones looked almost identical to related enzymes that can only modify auxin.

For more details, read the news release at Washington University in St. Louis website.