Cucumopine Type Agrobacterium Rhizogenes K599 (ncppb2659) T-dna Mediated Plant Transformation and Its Application

Agrobacterium rhizogenes infects plants to induce hairy roots. It is classified into four different types such as agropine, mannopine, cucumopine and mikimopine. A.rhizogenes K599, also known as NCPPB2659, is a representative strain of the cucumopine type. In this review, we discussed the functions of 11 genes on the T-DNA of Ri plasmid pRi2659 in K599. We summarized the infectivity of K599 on a variety of plants and reviewed the applications of K599-induced hairy roots. These applications include analyses of gene and recombinant plasmid functions, direct employment as root parasite host and model system for the interaction between root and its parasite, production of herbal active ingredients as bioreactor, and the regeneration of transgenic plant. We also prospected the application potentials of A. rhizogenes K599 in transgenic plant and the mechanism of K599-mediated transgenic plant. Introduction Agrobacterium rhizogenes is a gram-negative soil bacterium that belongs to the genus Agrobacterium and family Rhizobiaceae with an optimum growth temperature of 28oC (White and Nester 1980). It infects plants to induce hairy roots from the infection site, which is a result of the integration of T-DNA of the Ri plasmid of A. rhizogenes into plant genome (Chilton et al. 1982; Giri and Narasu 2000). The hairy roots harbor certain morphological characters, which roots are branched, pleiotropic and grow quickly on medium without plant hormones. Besides, hairy roots are maintaining the characteristics of the ordinary root system anatomically, and possesses highly stable hereditary since they originate from single-cells containing no chimeras (Banerjee et al. 2012, Peebles et al. 2009). According to opines production after infection, A. rhizogenes is classified into four different types, namely agropine, mannopine, cucumopine, and mikimopine. The Ri plasmid in the agropine type A. rhizogenes has two T-DNA regions TL-DNA (15-20 kb) and TR-DNA region (more than TL-DNA in length) that are linked by non-insertion region. The other three types of T-DNA is one-single continuous region in Ri plasmid containing rol genes and opine synthesis genes but no auxin synthesis genes (Combard et al. 1987, Kiyokawa et al. 1994, Guillon et al. 2006). Genes and their functions on the T-DNA of Ri plasmid of A. rhizogenes K599: K599 as a representative strain of cucumopine type A .rhizogenes, was isolated from soil by an Australian scholar, Allen Kerr (Savka et al. 1990). It contains endogenous Ri plasmid pRi2659 which is 185,462 bp in length with a 14,982 bp T-DNA (GenBank accession number: EU186381). The TDNA region contains a total of 11 genes/ORFs, which are orf2, orf3, orf4, orf8, rolA, rolB, rolC, rolD (orf13), rolE (orf13a), orf14 and cus, with orf4 being nested in orf3 (Fig. 1) (Mankin et al. 2007). ∗Author for correspondence. . Zhejiang Provincial Key Laboratory for Genetic Improvement and Quality Control of Medicinal Plants, Hangzhou-310036, China.