新型杀虫蛋白的发现

      Bt菌是抗虫转基因作物中杀虫基因的主要来源。Bt蛋白在20年来的转基因商业化应用过程中发挥了重要的作用。然而，由于昆虫对杀虫蛋白抗性的产生，抗虫作物的研发者迫切需要找到新的替代品。最近，杜邦先锋公司的研发人员从粪产碱杆菌（Alcaligenes faecalis）找到了一种新的玉米根甲虫杀虫蛋白AfIP-1A/1B，为以后培育新的抗根虫转基因玉米奠定了基础。

      AfIP-1A/1B蛋白是杜邦先锋的研究人员通过大规模筛选众多细菌菌株后找到的一个双组分蛋白。该蛋白特异性地对鞘翅目昆虫有毒杀活性。含有该蛋白的转基因玉米对地下害虫根甲虫防治效果明显。结构和功能分析表明，AfIP-1A/1B与Cry34Ab1/Cry35Ab1蛋白的结构和作用模式类似。
      最早的玉米根虫杀虫蛋白Cry3Bb1和Cry34Ab1/Cry35Ab1分别是孟山都公司和陶氏益农公司发现的，相应的转基因玉米（MON863和DAS59122）已商业化种植多年。随着玉米根虫对这两个蛋白抗性的产生，近年来孟山都公司利用RNAi技术开发了能够干涉昆虫DvSnf7基因从而达到防治效果的转基因玉米MON87411。
      70年Bt制剂的施用和20年Bt转基因作物的推广导致越来越多的昆虫种群对Bt蛋白产生了抗性。从另外的微生物菌株中发现对昆虫有毒杀效果的蛋白将是未来解决昆虫抗药性的一条有效途径。2016年，杜邦先锋公司从假单胞杆菌中发现了IPD072Aa，再加上本次发现的AfIP-1A/1B，表明了其在玉米根虫杀虫蛋白上的丰富储量。
Sci Rep. 7 (1): 3063; 2017 Jun 8
An Alcaligenes strain emulates Bacillus thuringiensis producing a binary protein that kills corn rootworm through a mechanism similar to Cry34Ab1/Cry35Ab1.
Author
Yalpani N, Altier D, Barry J……Xie W, Liu L, Wu G.
DuPont Pioneer, USA.
Abstract
Crops expressing Bacillus thuringiensis (Bt)-derived insecticidal protein genes have been commercially available for over 15 years and are providing significant value to growers. However, there remains the need for alternative insecticidal actives due to emerging insect resistance to certain Bt proteins. A screen of bacterial strains led to the discovery of a two-component insecticidal protein named AfIP-1A/1B from an Alcaligenes faecalis strain. This protein shows selectivity against coleopteran insects including western corn rootworm (WCR). Transgenic maize plants expressing AfIP-1A/1B demonstrate strong protection from rootworm injury. Surprisingly, although little sequence similarity exists to known insecticidal proteins, efficacy tests using WCR populations resistant to two different Cry proteins show that AfIP-1A/1B and mCry3A differ in their mode of action while AfIP-1A/1B and the binary Cry34Ab1/Cry35Ab1 protein share a similar mode. These findings are supported by results of competitive binding assays and the similarity of the x-ray structure of AfIP-1A to Cry34Ab1. Our work indicates that insecticidal proteins obtained from a non-Bt bacterial source can be useful for developing genetically modified crops and can function similarly to familiar proteins from Bt.