Effects of gibberellin 2-oxidase, phytochrome B1, and BAS1 gene transformation on creeping bentgrass photomorphogenesis under various light conditions

Sunlight is the primary energy source to drive photosynthesis, as well as the signal to stimulate series of developmental events ranging from germination to flowering in plants. Light can induce leaf formation, leaf expansion, and chloroplast differentiation, and inhibit stem elongation. Light has great impact on turfgrass quality and turfgrass performs best with a minimum of four to six hours of full sun per day. However, under certain circumstances, a grassed area may be shaded for most or all of the day, making it a problem for turfgrass to obtain enough light energy. Modern stadiums create a shaded environment that requires turfgrass for sports usage, while some area of a semi-enclosed arena receives little or no direct sunlight especially during winter season. Moreover, when sunlight penetrates the canopies and reaches the surface of the turf, both light quantity and quality (red/far-red ratio) drop dramatically. Shade stress causes succession of harmful physiological and morphological changes in plants, such as thinner, more delicate leaves, reduced tillering, poor shoot density, altered pigment concentration, and affected carbohydrate reserve. Moreover, it is difficult for turfgrass to recover from wear under shade.; Vertical growth remains a critical problem in turfgrass management. Practical methods can be used to control the plant growth. For example, application of chemical regulators can inhibit gibberellin (GA) biosynthesis and reduce the stem growth. Alternatively, improving the characteristics of cultivars by biotechnology is a long-term option. GA 2-oxidase (GA2ox) genes are important in control of GA levels. Overexpression of OsGA2ox causes a dwarf phenotype and delay in reproductive development in transgenic rice. Moreover, genetic engineering of phytochrome genes has provided a potential means to control vegetative growth and reproductive development. Phytochrome represents a family of red-light-absorbing photoreceptors that exist in the physiologically inactive Pr form and the active Pfr form. Transformation and overexpression of the PHYB gene in Arabidopsis and tobacco resulted in a dwarf phenotype. Additionally, BAS1 is a gene regulating brassinosteroid (BR) levels and light responsiveness in Arabidopsis. Overexpression of the BAS1 gene leads to decreased BR levels and a BR-deficient dwarf phenotype.; The objectives of our studies were: (1) develop creeping bentgrass plants transformed with GA2ox gene from runner bean ( Phaseolus coccineus), BAS1 gene from Arabidopsis , and PHYB1 gene from tobacco (Nicotiana tabacum), respectively; (2) evaluate growth responses of transgenic plants under various light conditions and reveal possible interactions between hormones and photo-receptors.; Our results showed that vertical growth, internode extension, and leaf growth of transgenic creeping bentgrass plants were inhibited by GA2ox transformation under reduced low light conditions in the field. True GA2ox gene transformants showed increase in overall quality, shoot density, or stolon density compared with control plants. Moreover, GA2ox transgenic lines tended to keep horizontal growth habit, possibly due to the increased GA metabolism by GA2ox overexpression, or the collaborated work of GA and light receptors in signal transduction. Greenhouse studies revealed the similar results to field studies. Strong transformants, such as GA6548 and GA6549, displayed dwarfism and superior quality under all light conditions. RT-PCR results confirmed that mRNA level of foreign GA2ox was correlated with the selection indices ranking of creeping bentgrass plants both in the greenhouse and the field.; Furthermore, reduction in R:FR increased vertical growth and erectness of both PHB1 gene transformants and control plants. As group, transgenic plants exhibited delayed vertical shoot growth and more horizontal shoot architecture, but did not demonstrate significant change in leaf growth or visual quality. PB0701 exhibited high...