What do the birch trees of New Hampshire have in common with us? Each species can attest a long and independent evolutionary history, in which both lineages separately invented multicellularity. To specify the spatial and temporal development of tissues, plants and animals have developed hormones to synchronize cellular events. As Biology Department professor Eric Schaller writes in his commentary, “Ethylene and the regulation of plant development,” our understanding of plant hormones is furthered by the recent discovery of a new role for ethylene in specifying the timing of leaf development. Schaller’s commentary was recently published in BMC Biology.
Antagonism between plant hormones produced in distinct tissues at distinct times is a method plants use to coordinate cell differentiation during development and to regulate adult growth. In the article that Schaller’s commentary addresses, “The embryonic leaf identity gene FUSCA3 regulates vegetative phase transitions by negatively modulating ethylene-regulating gene expression in Arabidopsis,” a group mostly composed of researchers from Canada describe misexpression and knockout mutants of the gene FUSCA3 in the plant model Arabidopsis.
By observing the changes in leaf structure that typically occur in Arabidopsis as the plant matures—leaves with embryonic features are usually found towards the base of the plant—the plant biologists determined that FUSCA3 mutants developed more adult-like leaves lower down on the plant. By simultaneously manipulating ethylene response pathways using mutations and drugs, including silver, embryonic features of the lower leaves can be restored, indicating antagonism between ethylene and FUSCA3.
Not only does the study reveal a new regulatory mechanism acting on ethylene, but it also suggests that ethylene has a new role: promoting adult-type leaf development. Ethylene, a gaseous molecule whose role as a plant hormone was first suggested by the senescence of plants near newly appearing street lamps in the nineteenth century, is known to govern a variety of maturation and aging processes in plants. Ripening of fruit, leaf abscission, senescence and antagonism towards the growth promoting effects of auxin are all known ways in which ethylene functions to mature plant tissues. Ethylene also regulates the famous “triple response” in seedlings fighting to emerge to the upper world, promoting horizontal growth around obstacles by stem lengthening, thickening and increasing curvature.
Schaller’s lab at Dartmouth is contributing to the growing knowledge base of plants’ complex hormonal regulatory networks through research on ethylene and cytokinin signal transduction. In a recent research report by his lab published in PLoS ONE, “Ethylene receptors function as components of high-molecular-mass protein complexes in Arabidopsis,” the behavior of the ethylene receptor ERS1 upon binding ethylene is shown to be reminiscent of the tyrosine kinases in animals, both of which form multi-protein complexes after activation. The perception and response of biological pathways to plant hormones is a fascinating subject of study, revealing commonalities and differences between animals and plants as they each developed techniques to control development and growth.