2017 ASHS Annual Conference

Cornus L. consists of approximately 55 species that are all horticulturally valuable trees, shrubs, or rarely perennial herbs with woody rhizomes, such as C. florida, C. kousa, C. mas, C. officinalis, C. sericea, C. sanguinea, C. controversa, and C. canadensis. The ornamental value is largely attributed to the spectacular structure or color of inflorescences, fruits, stems, or leaves. Some species are highly popular garden plants, especially C. florida. Natural populations of C. florida is however severely threatened by fungal diseases. Through analyses of genotyping by sequencing (GBS) and non-targeting metabolite profiling using LC-MS for populations growing in divergent natural environments, we identified loci under natural selection for local adaptation as well as loci and metabolites associated with disease. Furthermore, we also found fungal sequences detected by GBS in a plant was predictive of the disease condition. To understand the genetic control of inflorescence architectural variation and flower development in Cornus, we conducted comparative transcriptome analyses to identify candidate genes and evaluated the roles of putative key regulators through comparative gene expression analyses and genetic transformation. We found evidence supporting LFY, TFL1, and AP1 homologs in Cornus work together to regulate the determinate inflorescence development, but differential expression patterns of TFL1 and AP1 among species were important to the variation of inflorescence architectures among heads, umbels, dichasia, and elongated complex form. We also found evidence supporting an important role of MADS-box B class genes PI and AP3 homologs in flower development of Cornus and that proper expression of CorAP3 is critical to the origin of explosive pollen release uniquely evolved in the herbaceous perennial dogwood species occurring in circumboreal region. During the study of Cornus, we established an agrobacterium mediated stable genetic transformation system of C. canadensis (bunchberry) for validating gene functions. The transformation system in C. canadensis also provides a valuable tool for genetic manipulation to create new varieties of dogwoods that are horticultural interesting. Using the system, we generated a heat tolerant bunchberry that is sterile and can be a potential new ground cover garden plant for the south.