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Ghchi 6

Aphid is one of the most notorious economic pests in the world. They feed on phloem sap of the host plant and deprive the plant’s nutrients. They have a great impact on the plant’s yield. It is hard to control this kind of pest due to their small size and strong fertility. In addition, aphids control now rely on chemicals like pesticides that may allow the development of resistance. As a result, the aphids are harder to be controlled. Thus, developing a new way to control the aphid and promote yield is a general goal. So we introduce the aphid-resistance gene Ghchi6.

This gene is found in red chicken-feet cotton, and it belongs to Glyco-hydro-19's subfamily. This gene is composed of 975 bases and codes for the synthesis of class I chitinase which is made up of 324 amino acids.Its molecular weight is 34.65 k Da and isoelectric point is 7.81. Through amino acid sequence comparison, cotton gene Ghchi6 and other plant gene are highly conservative, and is evolutionarily close relative to chitin of woody cotton.

When the cotton is physically attacked by aphids, the gene Ghchi6 gets overexpressed that the plant starts to secrete chitinase. The overexpression of Ghchi6 can improve the aphid-resistance in cotton, and we plan to transfer this favored gene to tobacco to improve its aphid-resistance. Through modifications we have transferred the gene to Agrobacterium and then to a common tobacco Nicotiana rustica through infection. Normally the expression of chitinase in plants is very low under common conditions, but in cottons the expression is triggered by external factors like mechanical damage.

The aphids feed through their sucking mouthparts. The following graphs illustrate the expression levels of Ghchi6 gene in red-chicken feet cotton’s different parts (leaves, roots, stems) 24 hours after the attack from the aphids’ needling. As we can see, the expression of Ghchi6 occurs that all three parts are suppressed by the attack from aphids. This implies that the aphids have some specific techniques to control the expression of Ghich6 in plants to reduce the chitinase secrete by the plants. On the contrary, the pure mechanical stimulus like tearing part of the leave will trigger the overexpression of the gene, meaning that the protective mechanism has already started to secrete chitinase as the plant feels the threat from external environment. Although the aphid may use its saliva to reduce the expression of Ghchi6, it is still obvious that this gene can enhance the aphid-resistance.

In a paper named Functional study of cotton Chitinase gene Ghchi6 on the resistance to aphid which was done by Liang Luo and Prof. Chuanren Li, researchers transferred the gene Ghchi6 to a wild type of Arabidopsis to make a transgenic type. The Line 1, 2, and 4 have different expressions of the gene Ghchi6 in their leaves, and Line 4 has the highest expression, following by Line 1 and 2.

In the analysis of the Arabidopsis ‘s expression of chitinase, the figure clearly shows that all the transgenic types, Line 1, 2 and 4, are showing relatively higher chitinase activity, especially the Line 4 one which has a substantial improvement, implying that the overexpression of Ghchi6 is promoting the chitinase activity. Therefore the overexpression of Ghchi6 can enhance the plant’s aphid-resistance.

Sequence and Features