Plant architecture is a major consideration during the commercial production of chrysanthemum (Dendranthema grandiflora Tzvelev). We have addressed this problem through a biotechnological approach: genetic engineering of chrysanthemum cv. Iridon plants that ectopically expressed a tobacco phytochrome B1 gene under the control of the CaMV 35S promoter. The transgenic plants were shorter, greener in leaves, and had larger branch angles than wild-type (WT) plants. Transgenic plants also phenocopied WT plants grown under light condition depleted of far-red wavelengths. Furthermore, the reduction of growth by the expressed PHY-B1 transgene did not directly involve gibberellins. The commercial application of this biotechnology could provide an economic alternative to the use of chemical growth regulators, and thus reduce the production cost.
Zhi-Liang Zheng, Jyan-Chyun Jang, James D. Metzger and Zhenbiao Yang
Zhi-Liang Zheng, Zhenbiao Yang, Jyan-Chyan Jang and James D. Metzger
Height control is a major consideration during commercial production of chrysanthemum [Dendranthema×grandiflora Kitam. (syn. Chrysanthemum×morifolium Ramat.)]. We have addressed this problem by a biotechnological approach. Plants of `Iridon' chrysanthemum were genetically engineered to ectopically express a tobacco (Nicotiana tabacum L.) phytochrome B1 gene under the control of the CaMV 35S promoter. The transgenic plants were shorter in stature and had larger branch angles than wild type (WT) plants. Reduction in growth caused by the ectopic expression of the tobacco phytochrome B1 gene was similar to that caused using a commercial growth retardant at the recommended rate. Another morphological effect observed in the leaves of the transgenic plants was more intense green color that was related to higher levels of chlorophyll. The transgenic plants appeared very similar to WT plants grown under a filter that selectively attenuated far red wavelengths. Furthermore, when plants were treated either with gibberellin A3 (which promoted growth) or 2-chlorocholine chloride, an inhibitor of gibberellin biosynthesis (which inhibited growth) the difference in the average internode length between the transgenic plants and WT plants was the same in absolute terms. This suggests that reduction of growth by the expressed PHY-B1 transgene did not directly involve gibberellin biosynthesis. The commercial application of this biotechnology could provide an economic alternative to the use of chemical growth regulators, thereby reducing production costs.