Team:BNU-CHINA/Introduction

Team:BNU-CHINA - 2015.igem.org

1. Background

Nematode has been up to over 5000 of 200 genus[1]. Among them, over 100 species of nematodes are damaging the agricultural, forestal and economic crops of China who widely parasitize the roots, stems, leaves, flowers, buds and seeds of manifold plants, harming the development of agriculture and forestry seriously.

A newest research by USA indicates that the plant-parasitic nematodes damage leads to about 8 billion dollars’ losses to their croppers, which takes 12% of the whole value of the crop output. Meanwhile, according to incomplete statistics, the losses caused by paratrophy nematodes can reach 100 billion every year worldwide[2]. China’s researchers have done some relevant surveys as well, and according to incomplete statistics, 17 provinces such as Anhui, Hainan, Hubei, Gansu, Zhejiang and Fujian have reported root knot nematode disease once, among which the morbidity of some severe regions in Shandong province can up to 2/3[3]. Therefore we can note that plant-parasitic nematodes have brought out severe lost to global agriculture and forestry already.

Loss the Fig
Figure 1.hahahahah

The size of plant-parasitic nematodes is usually too small for naked eyes to catch sight of. In addition, the present survey about the agricultural damage of nematodes are so limited that people often fail to notice and prevent it in time. The plant-parasitic nematodes are furnished with scalpellus functioning to stab into the plant cells to obtain nutrients after seeking out the host with the amphids on their forehead, which as a result, could damage the host as well as bring in pathogenic fungus and therefore causing complex harm to them. Up to now, the pathogenesis of plant-parasitic nematodes can be concluded in theory as follow:

  1. The nematodes give raise to severe mechanical injury to the host plants when feeding on them with the scalpellus.
  2. Other pathogen accompanied with the nematodes induce plant disease.
  3. Some nematode secretion is toxic to the plants which as a consequence damages them.

In most canses, the mechanical damage by nematodes to host is a drop in the bucket, therefore the latter two theories are relatively common[4].

The majority of harmful nematodes in agriculture and forestry belong to Tylenchida while a little belongs to Dorylaimida. Meloisogyne spp. Heterodera spp. Aphelenchoides composticola, Ditylenchus dipsaci are nematodes that gravely damage plants around the world. Among them, Meloisogyne spp. mainly destroy the roots of plants by forming root-knot to hinder their development, which in turns, causes the roots rot. According to statistics, a slight Meloisogyne spp. disease can lead to a 20%~30% output reduction, and 50%~70% even a total loss if it’s severe. Heterodera spp. also target the roots of plants primarily, weakening and decomposing the roots. Ditylenchus dipsaci damage the underground part such as the tuber, tuberous root, bulb of the plants which results in their rot and malformation while some local part over ground would also be influenced to turn to malformation, ,Aphelenchoides composticola such as Bursaphelenchus xylophilus and Aphelenchoides besseyi generally aim at the overground part of plants who infect the leaves and causing lesion and leaf tip drying, and more than that, infect the trunks to kill the whole plant rapidly.

Hence one can see that plant-parasitic nematode cause serious losses to a variety of agricultural crops worldwide. Since the traditional methods based on the use of nematocides and antihelminthic drugs are associated with major environmental and health concerns, the development of biocontrol agents to control nematodes is of major importance[5]. In this case, our project is designed to control the losses caused by nematodes effectively and timely with biocontrol agents. And after the bait-kill system successfully established, we are looking forward to further expansion to other agricultural pests for the sake of achieving our ultimate goal – establishing a database containing attractant base and toxic protein base in allusion to all sorts of agricultural pests.

As to our project this year, we designed two models separately to attract and poison nematodes. We made E.coli synthesize limonene to bait plant-parasitic nematodes and then kill them with two kinds of toxic proteins Bace-16 and Mpl afterwards. Furthermore, we introduced a photo-regulated bi-direction transcription system to the whole system, by which means we would be able to regulate the .expression of attractant and toxic proteins through the control of light. That’s to say, the E.coli would express attractant to bait nematodes when exposed to light whereas express toxic proteins to kill them as a result of the promoter’s reverse in the dark.