TITLE:
Sweet Potato Leaf Curl Virus: Coat Protein Gene Expression in Escherichia coli and Product Identification by Mass Spectrometry
AUTHORS:
Dina Lida Gutierrez Reynoso, Rodrigo A. Valverde, Norimoto Murai
KEYWORDS:
Affinity Chromatography Purification, Coat Protein, Escherichia coli, Mass Spectrometry, Maltose Binding Protein, Sweet Potato Leaf Curl Virus
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.6 No.19,
December
7,
2015
ABSTRACT: Sweet potato is one of the first natural GMOs, genetically modified 8000 years ago by Agrobacterium
rhizogenes as reported recently by Kyndt et al. A section of 10 kbp long DNA (Transferred-
DNA or T-DNA) of the Ri (Root-inducing) plasmid was transferred to the plant genome by A. rhizo-genes and has been maintained in all 291 hexaploid sweet potato cultivars of the world. The maintenance
in the sweet potato genome and expression of two T-DNA genes for tryptophan-2-monooxygenease
(iaaM) and for indole-3-acetamide hydrolase (iaaH) are likely to be physiologically
significant since these enzymes convert tryptophan to indole-3-acetic acid, a major plant growth
hormone auxin. Sweet potato (Ipomoea batatas (L.) Lam) is ranked the third most important root
crop after potato and cassava, and the seventh in global food crop production with more than 126
million metric tons. Although sweet potato originated in Central or South America, China currently
produces over 86% of world production with 109 million metric tons. In the United States, North
Carolina is the leading producer with 38.5% of the 2007 sweet potato production, followed by California,
Mississippi, and Louisiana with 23%, 19%, and 15.9%, respectively. Leaf curl virus diseases
have been reported in sweet potato throughout the world. One of the causal agents is Sweet
potato leaf curl virus (SPLCV) belonging to the genus Begomovirus (family Geminiviridae). Although
SPLCV does not cause symptoms on Beauregard, one of the most predominant sweet potato cultivars
in the US, it can reduce the yield up to 26%. Serological detection of SPLCV is not currently
available due to the difficulties in obtaining purified virions that can be used as antigen for antiserum
production. In attempts to obtain the coat protein (CP) of SPLCV for antibody production,
primers were designed to amplify the CP gene. This gene was cloned into the expression vector
pMAL-c2E as a fusion protein with maltose-binding protein, and transformed into Escherichia coli strain XL1-Blue. After gene induction, a fusion protein of 72 kDa was purified by amylose affinity
chromatography. The yield of the purified fusion protein was approximately 200 μg/liter of bacterial culture. Digestion with enterokinase cleaved the fusion protein into a 42.5 kDa maltosebinding
protein and a 29.4 kDa protein. The latter protein was identified by mass spectrometry
analysis as the coat protein of SPLCV based on the fact that the mass spectrometry elucidated the
sequences corresponding to 37% of amino acid positions of the SPLCV coat protein.