Hongwei Du

An improved particle bombardment for the generation of transgenic plants by direct immobilization of relleasable Tn5 transposases onto gold particles

We have developed a modified particle bombardment method for plant transgenesis. An intein-tag and a 6×Cys-tag were successively fused to the N-terminus of a hyperactive Tn5 transposase. The modified transposase was immobilized on bare gold microscopic particles via covalent binding of a 6×Cys-tag sulfydryl groups to the gold surface. The tethered transposase can bind the transposon DNA in vitro to form the transposome in the absence of Mg2+ ions. After bombardment of the gold particles carrying the transposomes into the plant cells, the transposomes will be released from the carrier due to the activated self-cleavage function of intein-tag. Our data showed this procedure integrated foreign DNA into the plant genome with an increased transformation frequency as compared to the conventional particle bombardment method. A single copy insertion can also be obtained by decreasing of the assembled transposon DNA amount in relation to plant cell biomass.

Biodegradation of leuco derivatives of triphenylmethane dyes by Sphingomonas sp. CM9

A leuco derivatives of triphenylmethane dyes degrading bacterium, strain CM9, was isolated from an aquafarm field. Based on morphology, physiologic tests, 16S rDNA sequence, and phylogenetic characteristics, it was identified as Sphingomonas sp. This strain was capable of degrading leucomalachite green (LMG), leucocrystal violet and leucobasic fuchsin completely. The relationship between bacterium growth and LMG degradation suggested that strain CM9 could use LMG as the sole source of carbon. The most LMG degradation activity of CM9 crude extract was observed at pH 7.0 and at 30°C. Many metal ions had little inhibition effect on the degradation activity of the crude extract. CM9 also showed strong decolorization of triphenylmethane dyes to their leuco derivatives. GC/MS analysis detected two novel metabolic products, methylbenzene and 4-aminophenol, during the LMG degradation by CM9.

Tn5 transposase-assisted transformation of indica rice

Here, we describe experiments on Tn5 transposase-assisted transformation of indica rice. Transposomes were formed in vitro as a result of hyperactive Tn5 transposase complexing with a transposon that contained a 19-bp tetracycline operator (tetO) sequence. To form modified projectiles for transformation, the Tn10-derived prokaryotic tetracycline repressor (TetR) proteins, which can bind transposomes via the high affinity of TetR for tetO, were immobilized onto the surface of bare gold microscopic particles. These projectiles were introduced into cells of the indica rice cultivar Zhuxian B by particle bombardment. Once projectiles were inside the cell, tetracycline induced an allosteric conformational change in TetR that resulted in the dissociation of TetR from tetO, and thus generated free transposomes. Molecular evidence of transposition was obtained by the cloning of insertion sites from many transgenic plants. We also demonstrated that the introduced foreign DNA was inherited stably over several generations. This technique is a promising transformation method for other plant species as it is species independent.