The expression patterns of the clock genes period and timeless are affected by photoperiod in the Mediterranean corn stalk borer, Sesamia nonagrioides

Abstract

To obtain clues to the link between the molecular mechanism of circadian and photoperiod clocks, we cloned two circadian clock genes, period (per) and timeless (tim) from the moth Sesamia nonagrioides, which undergoes facultative diapause controlled by photoperiod. Sequence analysis revealed a high degree of conservation among the compared insects fοr both genes. We also investigated the expression patterns of per and tim in brains of larvae growing under 16L:8D (long days), constant darkness (DD) and 10L:14D (short days) conditions by qPCR assays. The results showed that mRNA accumulations encoding both genes exhibited diel oscillations under different photoperiods. The oscillation of per and tim mRNA, under short-day photoperiod differed from long-day. The difference between long-day and short-day conditions in the pattern of mRNA levels of per and tim appears to distinguish photoperiodic conditions clearly and both genes were influenced by photoperiod in different ways. We infer that not all photoperiodic clocks of insects interact with circadian clocks in the same fashion. Our results suggest that transcriptional regulations of the both clock genes act in the diapause programing in S. nonagrioides. The expression patterns of these genes are affected by photoperiod but runs with 24 h by entrainment to daily environmental cues.

The Cryptochrome1 (cry1) Gene has Oscillating Expression Under Short and Long Photoperiods inSesamia nonagrioides

“…In our study ( Figure 5) we showed that the Sncry1 mRNA peaked in the mid night comparable to Snper [11]. The discovery of the existence of two cry genes in moths and butterflies suggested that the clockwork mechanism of Lepidopteran insects differ from that of D. melanogaster [25].…”

“…We speculate that in insects maybe there is another possibility, such as in MCSB, where it seems that CRY1 alone, could evolve dual functions as transcriptional repressor and a photoreceptor. An interesting observation is that Snper, Sntim, Sncyc and Sncry1 synchronously peaked at midnight, revealing [11,12].…”

“…An established laboratory colony of S. nonagrioides, derived from field-collected larvae in Kopais (Latitude 38o 14΄, Central Greece) was used as experimental biological material. Larvae were reared on artificial diet and were grown under photoperiods of 16 h light (L): 8h dark (D) at 25±1°C and 65% relative humidity [11]. Photoperiods of 16L: 8D and continuous dark (DD) were used to encourage normal development while photoperiods of 10L: 14D were used to encourage diapause conditions.…”

“…In order to comprehend whether and how the circadian system is associated to photoperiodism, a significant piece of evidence is whether clock genes products oscillate and how they respond to a varying photoperiod [7][8][9]. The connection of circadian clock genes in diapause initiation has been debated [1,[10][11][12].…”

“…When diapause has been induced, larvae persist to grow and molt without pupating and up to six additional instars, elsewhere the normal five or six have been noticed, when larvae are continuous in diapausing conditions [11]. To accomplish indications to the link among the molecular mechanism of circadian and photoperiod clocks, in recent works we studied the expression of the clock genes period, timeless and cycle and the results suggested that transcriptional regulations of these clock genes act in the diapause programming in MCSB [11,12]. In the current study, we examined the contribution of cryptochrome1 (cry1) gene in the circadian rhythm and in the photoperiodic regulation of diapause in S. nonagrioides.…”