Weigel began to work with plants during his postdoctoral research with Elliot M. Meyerowitz at Caltech, where he cloned the floral regulator LEAFY from Arabidopsis thaliana. From 1993 to 2002, he was an Assistant and then Associate Professor at the Salk Institute for Biological Studies in La Jolla. In 2002, he accepted an appointment as Scientific Member and Director at the Max Planck Institute for Developmental Biology, where he founded the Department for Molecular Biology. He is also an Adjunct Professor at the Salk Institute and the University of Tübingen. In 2012, Weigel co-founded the plant bioinformatics startup company Computomics in Tübingen. He is a deputy editor of the eLife. During the 1990s, Weigel mostly studied the development of individual flowers and how the onset of flowering is regulated. His group made important discoveries in both areas. Together with Ove Nilsson, he demonstrated that transfer of the LEAFY gene from Arabidopsis thaliana to aspen trees was sufficient to reduce the time to flowering from years to months. Weigel and his team isolated the FT gene, which was later found to be an important component of the mobile signal inducing flowering. New genetic tools developed by his group led to the discovery of the first microRNA mutant in plants. Through his study of factors that control the onset of flowering, a quintessential adaptive trait, Weigel became interested in more general questions of evolution. Apart from work on genetic variation in environment-dependent developmental processes, his group is known for the generation of extensive genomic resources, such as the first haplotype map for a non-mammalian species. To further exploit and advance the understanding of genetic variation, Weigel and colleagues initiated the project for Arabidopsis thaliana. Related to this is a new area of interest, in genetic barriers. In collaboration with Jeffery Dangl, his group discovered that such barriers in plants are often associated with autoimmunity. They could show that in certain hybrid offspring, specific gene products contributed by one of the parents may be inappropriately recognized as foreign and pathogenic, and thus trigger pervasive cell death throughout the plant. Most of the causal genes encode components of the immune system, indicating that there are constraints on the assembly of an optimal immune system.
