Changes in gene expression in the leaf of Lolium temulentum L. Ceres during the photoperiodic induction of flowering

Abstract

Abstract. Unifoliated plants of Lolium temulentum L.Ceres were induced to flower by a unique 24-h long day (LD) consisting of the extension of the regular 8-h short day (SD) (400 I.tmol photons-m-2-s 1, fluorescence + incandescence) with incandescence at 10-15 gmolphotons. m-2.s-~. The polyadenylated-RNA complement of leaf blade tissues was analysed at 4-h intervals during the photoperiod extension in LD vs. SD, by using two-dimensional polyacrylamide gel electrophoresis to resolve in-vitro-translated products. Of the 991 spots that were analysed, none appeared or disappeared during the inductive cycle, i.e. no qualitative effect of floral induction was detected, at any time. Sixty-eight spots were found whose intensity was influenced by lengthening of the photoperiod; 50 of them, i.e. ca. 5% of the population analysed, were affected before the end of the extension period and were thus potentially related to floral induction. Many of these RNAs were not quantitatively constant during a 24-h cycle in SD. Seven of them oscillated according to the 'light-on' and the 'light-off" signals, among which three seemed to be controlled by phytochrome since their relative amount increased under the standard light conditions but decreased under incandescence even faster than in darkness. The large majority of other RNAs varied with a timing that was not clearly driven by the alternation of light and darkness, indicating that genes related to the biological clock may be especially sensitive to the lengthening of the photoperiod. Furthermore, seven spots were observed that underwent a phase-shift in LD, which consisted, for six of them, of a phase advance of 4-8 h. The steady-state level of CAB mRNA was analysed because the CAB gene family (encoding the chlorophyll a/b-binding proteins of the light-harvesting complexes) is known to be controlled both by the biological clock and phytochrome. In SD, the level was high in the light and low in Abbreviations: CAB = chlorophyll a/b-binding proteins of the light-harvesting complexes; 2D = two-dimensional; LD(s)= long day(s); LDP(s) = long day plant(s); SD(s) = short day(s); SDP(s) = short day plant(s) Correspondence to: C. P6rilleux; FAX: 32 (41) 66 38 31; E-mail: cperille@vm 1.ulg.ac.be darkness; the fluctuation was conducted by a circadian rhythm. When plants were exposed to the inductive LD, the peak of mRNA accumulation that was expected according to the endogenous rhythmicity was abolished, possibly because of the change in light quality during the LD extension.

Biological clocks in Arabidopsis thaliana

“…This is not rhythmic in all species and, where rhythmicity is observed, the circadian regulation can be transcriptional or post-transcriptional (Pilgrim & McClung, 1993). In addition, molecular screens aimed at identifying genes associated with photoperiodic floral induction have recovered a number of CCGs in Pharbitis nil (Zheng et al, 1993), Sinapis alba (Heintzen et al, 1994a,b) and Lolium temulentum (Perilleux et al, 1996). When fully sequenced, these RNAs will suggest the scope of circadian regulation in plant genomes.…”

Accumulation of a Clock-Regulated Transcript during Flower-Inductive Darkness in Pharbitis nil1

“…In most of the plant systems used in such studies, flowering can be induced by one photoperiodic treatment, which allows biochemical studies of the process (Bernier, 1988). Changes in biological activities, including changes in gene expression in leaves during photoperiodic treatments, have been studied in such plants (Heintzen et al, 1994a(Heintzen et al, , 1994bO'Neill et al, 1994;Ono et al, 1996;Périlleux et al, 1996). Because most plants in which photoperiodic flowering has been studied are LDPs, such as Arabidopsis, complementary studies of flowering of SDPs are particularly important at this time.…”