Plant & Animal Genomes XVI Conference

January 12-16, 2008
Town & Country Convention Center
San Diego, CA

The Circadian Clock And Timing Of Seasonal Growth In Hybrid Aspen

Iwanka Kozarewa , Mikael Johansson , Cristian Ibánez-Gutiérrez , Maria E. Eriksson

  Umea Plant Science Centre, Dept. of Plant Physiology, Umea University, SE-901 87 Umea, Sweden

The circadian clock is an endogenous biological timer, which is set to about 24 hours and keeps its rhythm by resetting itself to local time each day by the regular changes in light and temperature. In hybrid aspen (Populus tremula L. x P. tremuloides Michx., Ptt) the clock is important for synchronization of daily events but also, as shown, crucial for seasonal events such as growth cessation and bud set. The putative aspen oscillator genes LATE ELONGATED HYPOCOTYL 1 and 2 (PttLHY1 and PttLHY2), as well as TIMING OF CAB 1 (PttTOC1) have been knocked down in hybrid aspen using RNA interference (RNAi) and their resulting phenotypes was investigated by physiological assays, and quantitative real-time PCR. Also, plants carrying the heterologous Arabidopsis promoter COLD AND CIRCADIAN RHYTHM RNA BINDING 2 (CCR2) fused to firefly luciferase, enabled us to follow the expression of CCR2 in real-time by measuring the amount of emitted light reported by the luciferase. Strong down regulation of PttLHY, or PttTOC1 by RNAi results in trees with shorter internal periods. The shortening in period affects the phase of clock associated gene expression and leads to a shorter critical day length for growth in these trees. Thus, RNAi lines continue to grow when wild type trees stop under 15 hours light: 9 hours dark. Our studies show that the circadian clock is participating in deciding the critical day length for growth in aspen, and its implications for dormancy will be discussed.