Universal and differential transcriptional regulatory pathways involved in the preparation of summer and winter diapauses in Pieris melete

Transcriptome-based analysis reveals a crucial role of the 20E/HR3 pathway in the diapause of Pieris rapae

Pieris rapae is among the most damaging pests globally, and diapause makes it highly resistant to environmental stresses, playing a crucial role in the survival and reproduction of P. rapae while exacerbating the challenges of pest management and control. However, the mechanisms of its diapause regulation remain poorly understood. This research used RNA sequencing to profile the transcriptomes of three diapause phases (induction and preparation, initiation, maintenance) and synchronous nondiapause phases in P. rapae. During each comparison phase, 759, 1045, and 4721 genes were found to be differentially expressed. Among these, seven clock genes and seven pivotal hormone synthesis and metabolism genes were identified as having differential expression patterns in diapause type and nondiapause type. The weighted gene co-expression network analysis (WGCNA) revealed the red and blue modules as pivotal for diapause initiation, while the grey module was identified to be crucial to diapause maintenance. Meanwhile, the hub genes HDAC11, METLL16D, Dyw-like, GST, and so on, were identified within these hub modules. Moreover, an ecdysone downstream nuclear receptor gene, HR3, was found to be a shared transcription factor across all three phases. RNA interference of HR3 resulted in delayed pupal development, indicating its involvement in regulating pupal dipause in P. rapae. The further hormone assays revealed that the 20-hydroxyecdysone (20E) titer in diapause type pupae was lower than that in nondiapause type pupae, which exhibited a similar trend to HR3. When 20E was injected into diapause pupae, the HR3 expression levels were improved, and the pupal diapause were broken. These results indicate that the 20E/HR3 pathway is a critical pathway for the diapause regulation of P. rapae, and perturbing this pathway by ecdysone treatment or RNAi would result in the disruption of diapause. These findings provide initial insights into the molecular mechanisms of P. rapae diapause and suggest the potential use of ecdysone analogs and HR3 RNAi pesticides, which specifically target to diapause, as a means of pest control in P. rapae.

Diapause-Linked Gene Expression Pattern and Related Candidate Duplicated Genes of the Mountain Butterfly Parnassius glacialis (Lepidoptera: Papilionidae) Revealed by Comprehensive Transcriptome Profiling

The mountain butterfly Parnassius glacialis is a representative species of the genus Parnassius, which probably originated in the high-altitude Qinhai–Tibet Plateau in the Miocene and later dispersed eastward into relatively low-altitude regions of central to eastern China. However, little is known about the molecular mechanisms underlying the long-term evolutionary adaptation to heterogeneous environmental conditions of this butterfly species. In this study, we obtained the high-throughput RNA-Seq data from twenty-four adult individuals in eight localities, covering nearly all known distributional areas in China, and firstly identified the diapause-linked gene expression pattern that is likely to correlate with local adaptation in adult P. glacialis populations. Secondly, we found a series of pathways responsible for hormone biosynthesis, energy metabolism and immune defense that also exhibited unique enrichment patterns in each group that are probably related to habitat-specific adaptability. Furthermore, we also identified a suite of duplicated genes (including two transposable elements) that are mostly co-expressed to promote the plastic responses to different environmental conditions. Together, these findings can help us to better understand this species’ successful colonization to distinct geographic areas from the western to eastern areas of China, and also provide us with some insights into the evolution of diapause in mountain Parnassius butterfly species.

Characterization of Three Heat Shock Protein Genes in Pieris melete and Their Expression Patterns in Response to Temperature Stress and Pupal Diapause

Simple Summary

Pieris melete, a major pest of crucifers, undergoes obligatory diapause as pupae to survive unfavorable temperature extremes during hot summers and cold winters. Heat shock proteins 70 (Hsp70) participate in this process; however, little is known about the underlying changes in Hsp70 expression both during the summer and winter diapause. The study aimed to investigate expression patterns of Hsp70s (PmHsc70/PmHsp70a, b) in response to diapause and short-term temperature stresses. The results showed that the expression of PmHsc70 and PmHsp70b were upregulated both in summer and winter diapause. Heat shock significantly induced up-regulation of the three genes in both summer and winter diapause. In non-diapause pupae, none of the genes responded to cold or heat stress. Further, it was found that 39 °C for 30 min was the most sensitive heat stress condition for PmHsc70 expressions in summer diapause and all three genes’ expressions in winter diapause. During summer diapause, the expression of the genes was up-regulated in response to high temperature acclimation at 31 °C. Meanwhile, only PmHsp70a and PmHsp70b were up-regulated when acclimated to a low temperature of 4 °C in winter diapause. In conclusion, the current results indicate that PmHsp70s plays a crucial role during both summer and winter diapause, in response to temperature stresses; and our findings may contribute to the increasing knowledge on seasonal diapause adaption.

Abstract

Heat shock protein 70 genes participate in obligatory pupal diapause in Pieris melete to survive unfavorable conditions. In this study, three full-length cDNAs of PmHsc70, PmHsp70a and PmHsp70b were identified, and their expression patterns in response to diapause and short-term temperature stresses were investigated. Summer and winter diapause were induced in the pupae and non-diapause individuals were used as a control. The pupae from each diapause group were subjected to either hot or cold conditions and the expression levels of the HSP genes were measured. Our results showed that up-regulation of PmHsc70 and PmHsp70b were detected both in summer and winter diapause, but not for PmHsp70a. Under cold stress, PmHsp70a and PmHsp70b were upregulated in summer and winter diapause, while heat shock significantly induced upregulation of all three genes. In non-diapause pupae, none of the genes responded to cold or heat stress. Furthermore, we found that incubation at 39 °C for 30 min was the most sensitive heat stress condition for PmHsc70 expression in summer diapause. On the other hand, the same temperature was effective for PmHsc70, PmHsp70a, and PmHsp70b expression in winter diapause. During summer diapause, expression of all three genes was upregulated in response to high-temperature acclimation at 31 °C, but only PmHsp70a and PmHsp70b were upregulated when acclimated to a low temperature of 4 °C in winter diapause. These results suggest that the PmHsc70, PmHsp70a, and PmHsp70b respond differently to pupal diapause and temperature stress, and that PmHsc70 is more sensitive to heat shock than to cold stress.

Identification and up-regulation of three small heat shock proteins in summer and winter diapause in response to temperature stress in Pieris melete

Small heat shock proteins (sHSPs) are conserved proteins that play key roles in organismal adaptation to adversity stressors. However, little is known about sHSPs during summer diapause. Three sHSP genes: PmHSP19.5, PmHSP19.9, and PmHSP20.0 were identified and cloned from Pieris melete. Sequence alignment and phylogenetic analysis revealed that the three sHSPs have a typical, conserved α-crystallin domain. PmHSP19.5 and PmHSP20.0 were both upregulated in summer diapause (SD) and winter diapause (WD), compared to non-diapause (ND) pupae. All three sHSPs were upregulated and showed similar trends in response to thermal stress. The 0 °C chilling treatment slightly affected sHSP transcripts in ND pupae, whereas both PmHSP19.5 and PmHSP19.9 were upregulated and PmHSP20.0 was downregulated after chilling at 0 °C for 24-96 h in both SD and WD pupae. The transcripts of PmHSP19.5 and PmHSP19.9 were significantly induced at 31 °C for 30 d in SD and WD pupae. The PmHSP20.0 transcript gradually decreased during the SD and WD programs. This is the first time that sHSPs have been linked to both overwintering and summer diapause processes. These findings suggest that sHSPs are involved in both summer and winter diapause maintenance and play a possible key role in temperature stress.