Int. J. Mol. Sci. 2009, 10, 1896-1910; doi:10.3390/ijms10041896 International Journal of Molecular Sciences ISSN 1422-0067 www.mdpi.com/journal/ijms Article Overexpression of a Weed (Solanum americanum) Proteinase Inhibitor in Transgenic Tobacco Results in Increased Glandular Trichome Density and Enhanced Resistance to Helicoverpa armigera and Spodoptera litura Ming Luo 1,# , Zhaoyu Wang 1,# , Huapeng Li 1 , Kuai-Fei Xia 1 , Yinpeng Cai 1 and Zeng-Fu Xu 1,2, * 1 State Key Laboratory of Biocontrol and Key Laboratory of Gene Engineering of the Ministry of Education, School of Life Sciences, Sun Yat-sen University, Guangzhou 510275, Guangdong, P.R. China 2 Laboratory of Molecular Breeding of Energy Plants, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Kunming 650223, Yunnan, P.R. China # These authors contributed equally to this work * Author to whom correspondence should be addressed; E-Mail: zengfu.xu@gmail.com; Tel. +86-20-8411 2516; Fax: +86-20-8403 6551 Received: 12 March 2009; in revised form: 17 April 2009 / Accepted: 21 April 2009 / Published: 23 April 2009 Abstract: In this study we produced transgenic tobacco plants by overexpressing a serine proteinase inhibitor gene, SaPIN2a, from the American black nightshade Solanum americanum under the control of the CaMV 35S promoter using Agrobacterium tumefaciens-mediated transformation. SaPIN2a was properly transcribed and translated as indicated by Northern blot and Western blot analyses. Functional integrity of SaPIN2a in transgenic plants was confirmed by proteinase inhibitory activity assay. Bioassays for insect resistance showed that SaPIN2a-overexpressing transgenic tobacco plants were more resistant to cotton bollworm (Helicoverpa armigera) and tobacco cutworm (Spodoptera litura) larvae, two devastating pests of important crop plants, than the control plants. Interestingly, overexpression of SaPIN2a in transgenic tobacco plants resulted in a significant increase in glandular trichome density and a promotion of trichome branching, which could also provide an additional resistance mechanism in transgenic plants against OPEN ACCESS