Development of a compact garden mum variety through introduction of the BrSRS7 gene

Abstract

In general, most chrysanthemums are sold as cut flowers, although some are used for landscaping or potted plants, which are treated with aplant growth regulator (PGR) for miniaturization.A garden mum is a chrysanthemum variety that,like pot-type chrysanthemums, requiresseveral pinching and growth regulator treatments.The BrSRS7 gene was previously shown to reduce the plant height of chrysanthemums after being introduced into the Dohwaball garden mum variety. Three transgenic BrSRS7-overexpressing(BrSRS7OX)lineswere selected. Aftertwo subsequent rounds of vegetative propagation, the three lines exhibited reduced height. In the Do-59, Do-74, and Do-95BrSRS7 OX lines, the height was reducedby 29.4%, 42.7%, and 27.1%, respectively, compared to the control group. The largest average decrease (150 mm) was observed in Do-74 (control average 250 mm), while the average decrease in the other two lines was 180 mm.The length and width of the Do-74leaves also decreased by 32% and 29.8%, respectively.The flower diameter was decreased by about 12.9%. Semi-quantitative polymerase chain reaction (PCR) analysis revealed 1.5-fold or more overexpression of the BrSRS7 gene in all three lines. When cells of BrSRS7 OXstems were fixed and cut longitudinally, Do-50 cells exhibited the smallest size (70% smaller than the control), and were markedly smaller than Do-74 and Do-95 cells, which were 27.3% and 50.9% smaller, respectively, than the control. We investigated the expression of plant height-related genes in the BrSRS7OX plants. In all three lines, GA20 oxidase (GA20ox)expression was greatly reduced and GA3 oxidase (GA3 ox)expression was also decreased relativeto the control. GA2oxidase (GA2ox)expression was increased in the Do-74 and Do-95 lines relative to the control, and the expression of DELLA(GAI) was increased more than 1.5 times relative tothe control group in all three lines. Expression of YUCCA10,an auxin-related gene, and TSJT1, a stem-specific gene, also decreased in all the overexpression plants. Over expression of theBrSRS7 gene in the Dohwaball garden mum variety resulted insignificantly reduced plant height and a dome-shellgrowth habit phenotype without the need for pinching or PGR treatments.