Characterization of Shade-avoidance in Chrysanthemum and Genetic Transformation with Phytochrome-A from Oat

Abstract

Shade-avoidance in plants can result in tall, spindly, and unmarketable plants. Because plant spacing and shade can signal shade avoidance, we grew chrysanthemum (Chrysanthemum grandiflora Ramat, cv. Nob Hill) under two planting densities to characterize the normal plant response to crowding. Plants grew 72 ± 4 cm and developed 17 ± 3 floral branches under 55-cm spacing, while plants grown in close proximity (15-cm centers) grew 78 ± 3 cm and developed 7 ± 1 floral branches under a 12-hour photoperiod. Because phytochrome-A overexpression is known to create dwarf plants, we were interested in transforming `Nob Hill' to alter its phenotype. Sterile leaf and stem cuttings of `Nob Hill' were transformed to express phytochrome-A (Phy-A) from oat (provided by R. Vierstra) using Agrobacterium tumefaciens. The method of Ledger et al. [Plant Cell Reports 10:195 (1991)] was improved when we used internodal segments as described by Yepes et al. [Plant Cell Reports 14:694 (1995)] for a 58% regeneration efficiency. Transformants were screened by selective media and confirmed by southern blots using monoclonal antibodies provided by R. Vierstra. Transgenic and control plants were grown in a greenhouse at 20°C day and 18°C night temperatures with a 14-hour photoperiod. At 4 weeks old, transgenic plants (11 ± 2 cm) were shorter than control plants (15 ± 3 cm). The use of this new transgenic chrysanthemum for high-density mum production is discussed.