Three biotechnological methods to develop compact ornamentals
Henrik Lütken, Ph.D, Associate Professor
Department of Plant and Environmental Sciences, Copenhagen University
Plant height is a quality parameter of primary importance in a large number of economically important ornamental plants. Consumers prefer short, compact plants with good keeping quality and ornamental value. In addition, compact plants tolerate mechanical handling and transport far better than more elongated plants. Furthermore, smaller plants require less space in expensive production facilities, are easier to handle, have reduced transportation costs and advantages for retailers. Thus, compact plants are preferred throughout the whole production and postharvest chain increasing profit in production and distribution. Currently, the feature compactness is obtained through the extensive utilization of chemical growth retardation targeting gibberellin (GA) response, e.g. chlormequat, daminozide or paclobutrazol. The number of approved growth retardation compounds is highly dependent on the country of production. For example, application of paclobutrazol and daminozide is no longer approved in many European countries. In my talk I’ll present and discuss three biotechnological methods; a non-GMO, a cisgenic and a GMO approach to develop compact ornamentals exemplified by Kalanchoë. In the non-GMO method unmodified strains of the soil-born bacterium Agrobacterium rhizogenes are used for transformations and this method is not considered as a GMO method in the European Union and Japan. Using this method compact plants are produced by the insertion of T-DNA containing root loci (rol) genes from A. rhizogenes into potted plants. Infection of plants by A. rhizogenes induces the growth of hairy-roots at the infection sites due to the insertion of four rol-genes, rolA, rolB, rolC and rolD. In many ornamental plants, rol-genes have been successfully used, causing reduced plant height, short internodes and reduced apical dominance. The cisgenic approach involves KNOX (KN) homeotic proteins that generally are involved in stem meristem differentiation. These genes can be used to modify plant architecture by both overexpression and silencing. The compact plants derived from this method often show a higher degree of branching and darker green colour due to elevated chlorophyll content. The latter is a highly desired feature in the ornamental plant industry. In the GMO approach the Short Internodes (SHI) gene from the model plant Arabidopsis thaliana is ectopically expressed. The SHI gene encodes a transcription factor belonging to the SHI–gene family, where the members act by gene dose-effect and are partially redundant. Overexpression of the genes leads to compact plants with a phenotype of mutants defective in GA biosynthesis and response. Although flowering can be delayed it can be restored by application of minute amounts of GA. When expressed in ornamentals compact inflorescences were in particular observed.
