지난 10년 동안, 이중 가닥 RNA (double-stranded RNA, dsRNA)를 이용한 특정 유전자 발현 간섭(RNA interference, RNAi) 기술은 의약품 개발뿐만 아니라 작물보호 분야에 해충방제부터 익충보호까지 다양하게 그 기술이 사용되어 왔다. 그동안 학계 및 산업체에서 활발히 연 구되어 온 RNAi기술을 이용한 작물 및 익충보호제는 상용화를 눈앞에 두고 있다. 미래 농업 시장에서 해충방제제와 익충보호제로써의 개발을 위한 RNAi의 기술적 응용은 상당한 잠재력을 가지고 있지만, 현장에 직접 사용되기에는 아직 여러 가지 한계점이나 극복해야 할 과제가 남아있 다. 본 리뷰에서는 최근에 활발히 진행되고 있는 작물보호제 및 익충보호제(protection of crops and beneficial insects)로써의 dsRNA의 다양 한 활용과 그 잠재성(potential)을 소개하고자 한다.

신경펩타이드(Neuropeptide)는 신경세포에서 분비되는 단백질성 물질로, 곤충 호르몬에서 가장 큰 그룹으로 차지한다. 이들은 곤충의 전 생육단계에 걸쳐 지방체의 항상성, 섭식, 소화, 배설, 순환, 번식, 탈피/변태 등 다양한 생리적 기능과 행동을 조절하는데 관여하고 있다. 신경호 르몬 일종인 PRXamide (NH2) 펩타이드 계열 호르몬은 카르복실기 끝에 PRX (X, 다양한 아미노산)라는 공통의 아미노산 서열이 특징적으로 존재하고 있으며, 곤충 전반에 걸쳐 발견된다. 곤충에서PRX 신경호르몬은 다양한 생물학적 기능에 관련하고 있는데 호르몬구조와 기능에 따라 크게 3가지로 분류한다. Pyrokinin (PK)계열의 호르몬은 페로몬 생합성 활성화 신경펩타이드(pheromone biosynthesis activating neuropeptide, PBAN) 및 휴면 호르몬(diapause hormone, DH)이 속하며, 카파(CAPA) 펩타이드 호르몬, 그리고 탈피촉진 호르몬(ecdysis trigging hormone, ETH)이 여기에 속한다. PK 계열의 PBAN 호르몬은 지금으로부터 약 30년전 나방에서 처음 밝혀졌으며, 성페로몬 생합성 을 자극하는 신경호르몬으로 확인되었다. 그 이후, PBAN의 연구는 절지동물 전반에 걸쳐 다양한 연구자들에 의하여 광범위하게 이루어졌다. 본 종설은 PBAN의 유전자 구조와 발현, PBAN에 의한 세포신호 전달과 성페로몬 생합성에 관련된 생리적 기작, 그리고 신경호르몬과 PBAN을 이용한 새로운 해충 방제법 개발의 가능성과 예를 소개한다.

RNA interference (RNAi) technology is a new direction for insect pest management, a biologically-based and target specific strategy. During the past decade the availability of insect genomics and computational biology has further enabled the implementation of RNAi technology to target economically important insect pests. It has shown striking results in various insect groups, suggesting that it will be a promising tool for the next generation of pest management. The mechanism of RNAi action is a specific knockdown of gene expression vie degradation of a target messenger RNA (mRNA), by double-stranded RNA (dsRNA). The applied dsRNA thus blocks target protein synthesis, leading to failure of normal physiological functions in the organism To successfully develop RNAi applications, a critical initial step is screening for appropriate candidate genes to identify RNAi targets, because the impacts of gene silencing (especially in terms of which other genes are effected) vary for different RNAi target genes and insects. The challenge with gene selection is to select suitable insect-specific target genes that provide fast-acting mortality or suppression and long-term population suppression without affecting other non-target organisms.

Currently, major controlling tools for insect pests depend on conventional chemical insecticides and genetically-modified organisms. These methods target neuro-synapses, channels and/or receptors that result in neurotoxicity or physiological imbalance. Unfortunately, this mode of action affects non-target animals and difficult to control insect species-specific. The application of classic insecticides is more and more restricted due to many problematic side effects, such as human and environmental toxicity, non-target insect and animal effects, and resistance. During the past decades new genomics/proteomics technologies such as RNA interference (RNAi), allow development of new classes and/or mode of action of insecticides and functionally screen bioactive compounds. Insect neuropeptides are the largest group, more than 90%, of all insect hormones that are involved in almost all physiological functions during the developmental and adult stages. Therefore, insect neuropeptide hormones and their receptors are good targets for discovery of insecticides such as RNAi and bioactive agents. In the presentation, insect case studies using neuropeptides and receptors suggest the possibility of novel biologically-based insect pest control methods.

Neuropeptides are the largest group of neurohormones that act in intercellular communication to regulate various physiological and behavioral events during development and reproduction in animals. One of these families is Pyrokinin/PBAN (Pheromone Biosynthesis Activating Neuropeptide) family defined by a similar 5-amino-acid C-terminal sequence (FXPRLamide) that is the active core fragment for these peptides. This motif has been identified from a variety of insect orders, and even a crustacean species. This family of peptides has been implicated in various physiological functions: 1) moth pheromone biosynthesis, 2) larval melanization, 3) moth embryonic and pupal diapause, 4) visceral muscle contraction in the cockroach, 5) fly puparium formation in different insect species. To date, ~159 PBAN/Pyrokinin family peptides have been identified from 40 species. It is one of the largest neuropeptide families in insects; however, the physiological function of most of these peptides is unknown. The mechanism of PBAN control over pheromone production is only well defined for sex pheromone biosynthesis in a limited number of lepidopteran moths. No other insect groups have been reported to regulate pheromone biosynthesis using PBAN. Conventional insecticides target synapses and/or sodium channels that result in neurotoxicity in the nervous system. Unfortunately, this mode of action affects non-target animals as well. These methods remain the major tool for pest control, and the side effects cause many global problems that result in increased environmental and human health expenses. Therefore, we are faced with a requirement to develop new targeted control agents that will lead to pesticides with new modes of action. This is not impossible, but not easy. Every species-specific neuropeptide is expected to play a critical physiological function in metamorphosis and development of insects. There are no exceptions. Our long-standing question is – “how can interference/disruption ofthe insect (neuro)hormonal system be used to discover novel control tools”. To solve this question a novel approach is being applied for finding and screening novel agonist and/or antagonist to gene products, neuropeptide and receptor, from the in vitro system and through virtual modeling. This concept will be a new paradigm opening the window for the next generation of the pest control, and the principle method will be adapted for insect specific pests. Another research interest here will be presented on exocrinal products, such as semiochemicals produced from insects and plants for chemical communication that regulates insect/insect and insect/host interactions. These studies have included the identification of pheromones and the biosynthetic pathway of their production from insects. The ultimate goal of this research is to discover novel biologically-based green pesticides that are environmental-friendly pest control alternatives.