Cheng Bei-jiu

A Preliminary Study on DNA Mutation Induction of Maize Pollen Implanted by Low Energy N+ Beam

The maize pollens were implanted with seven different doses of 30 keV N+ beam respectively, The genomic DNA polymorphism from treated pollens were analyzed with 104 primers by using RAPD respectively. The results showed that N+ beam-induced mutation of maize pollens can result in the change of their DNA bases. The mutation is not properly random and its frequency increases with a rise in 30 keV N+ beam doses. It is conformed with A-G transformation, which is one of the most important factors in DNA bases induced by N+ beam.

Genome-wide analysis of NBS-encoding disease resistance genes in maize inbred line B73.

Nucleotide-binding site(NBS) disease resistance gene is a largest category in plant disease resistance genes,which is a focus in recent studies on molecular breeding of plant disease resistance.Using maize(Zea mays L.) inbred line B73,the complete set of disease resistance candidate genes that encode NBS was identified in the genome.The putative NBS genes were characterized with respect to structural diversity,phylogenetic relationships and so on.One hundred and sixty-five NBS-coding sequences were identified into two types:nonregular(12) and regular NBS genes(153).The amount of NBS genesis much smaller in maize than in japonica rice(Oryza sativa L.).The 153 regular NBS genes were categorized into eight classes,including CC-NBS-LRR,CC-NBS,NBS,NBS-NBS,NBS-LRR,NBS-NBS-LRR,NBS-X,and X-NBS,according to N-terminal motif and leucine-rich repeat(LRR) domains motif.The 165 NBS genes showed two remarkable branches in the phylogenetic tree,differing from the radiation structure in japonica rice.Gene duplication event was observed based on gene family analysis of the NBS disease-resistance genes in maize;however,the ratio of gene duplication was smaller than that in rice.This might be one of the reasons for less NBS disease-resistance genes in maize than in rice.

Preliminary Studies on Base Substitutions and Repair of DNA Mismatch Damage Stimulated by Low Energy N+ Ion Beam Implantation in Escherichia coli

Ever since the low energy N+ ion beam has been accepted that the mutation effects of ionizing radiation are attributed mainly to direct or indirect damage to DNA. Evidences based on naked DNA irradiation in support of a mutation spectrum appears to be consistent, but direct proof of such results in vivo are limited. Using mutS, dam and/or dcm defective Eschericha coli mutator strains, an preliminary experimental system on induction of in vivo mutation spectra of low energy N+ ion beam has been established in this study. It was observed that the mutation rates of rifampicin resistance induced by N+ implantation were quite high, ranging from 9.2 × 10-8 to 4.9 × 10-5 at the dosage of 5.2 × 1014 ions/cm2. Strains all had more than 90-fold higher mutation rate than its spontaneous mutation rate determined by this method. It reveals that base substitutions involve in induction of mutation of low energy nitrogen ion beam implantation. The mutation rates of mutator strains were nearly 500-fold (GM2929), 400-fold (GM5864) and 6-fold larger than that of AB1157. The GM2929 and GM5864 both lose the ability of repair DNA mismatch damage by virtue of both dam and dcm pathways defective (GM2929) or failing to assemble the repair complex (GM5864) respectively. It may explain the both strains had a similar higher mutation rate than GM124 did. It indicated that DNA cytosine methylase might play an important role in mismatch repair of DNA damage induced by N+ implantation. The further related research were also discussed.

The Breeding of a Pigment Mutant Strain of Steroid Hydroxylation Aspergillus Flavus by Low Energy Ion Implantation

In the process of the fermentation of steroid C11α-hydroxylgenation strain Aspergillus flavus AF-ANo208, a red pigment is derived, which will affect the isolation and purification of the target product. Low energy ion beam implantation is a new tool for breeding excellent mutant strains. In this study, the ion beam implantation experiments were performed by infusing two different ions: argon ion (Ar+) and nitrogen ion (N+). The results showed that the optimal ion implantation was N+ with an optimum dose of 2.08 × 1015 ions/cm2, with which the mutant strain AF-ANm16 that produced no red pigment was obtained. The strain had high genetic stability and kept the strong capacity of C11α-hydroxylgenation, which could be utilized in industrial fermentation. The differences between the original strain and the mutant strain at a molecular level were analyzed by randomly amplified polymorphic DNA (RAPD). The results indicated that the frequency of variation was 7.00%, which would establish the basis of application investigation into the breeding of pigment mutant strains by low energy ion implantation.

Creation of High-Yield Polyhydroxyalkanoates Engineered Strains by Low Energy Ion Implantation

Polyhydroxyalkanoates (PHAs), as a candidate for biodegradable plastic materials, can be synthesized by numerous microorganisms. However, as its production cost is high in comparison with those of chemically synthesized plastics, a lot of research has been focused on the efficient production of PHAs using different methods. In the present study, the mutation effects of PHAs production in strain pCB4 were investigated with implantation of low energy ions. It was found that under the implantation conditions of 7.8 × 1014 N+/cm2 at 10 keV, a high-yield PHAs strain with high genetic stability was generated from many mutants. After optimizing its fermentation conditions, the biomass, PHAs concentration and PHAs content of pCBH4 reached 2.26 g/L, 1.81 g/L, and 80.08% respectively, whereas its wild type controls were about 1.24 g/L, 0.61 g/L, and 49.20%. Moreover, the main constituent of PHAs was identified as poly-3-hydroxybutyrates (PHB) in the mutant stain and the yield of this compound was increased up to 41.33% in contrast to that of 27.78% in the wild type strain.