How Do Plant Galls Form?
The gall-inducers (insects, mites, fungi, bacteria, viruses, nematodes, and other organisms) release molecules that modify hormone biosynthesis, transport, perception, or downstream gene expression. These molecules alter the balance between plant growth hormones such as auxin and cytokinin, while often suppressing defense hormones like jasmonic acid.
- Growth hormones like auxin and cytokinin regulate cell division, tissue differentiation, and organ formation.
- Defense hormones like jasmonic acid helps coordinate the plant's defense against herbivores and pathogens.
These molecular signals cause the plant to grow galls as highly specialized organs, supplying nutrients, protection, and a favorable biochemical environment for the organism that induced it.
Many details remain unknown, and different gall-inducing organisms appear to use different molecular strategies. Despite this diversity, the underlying principle is consistent: an external organism reprograms the plant's developmental machinery to grow a novel organ for its own benefit.