Pan Guangtang

Genetic diversity based on SSR markers in maize (Zea mays L.) landraces from Wuling mountain region in China

Genetic diversity of maize (Zea mays L.) plays a key role in maize breeding (William and Michael 2002). Knowledge of the amount and the distribution of genetic variation within and among maize landraces will provide a guide for predicting the degree of inheritance, variation, and level of heterosis, that are essential for maize breeding (Duan et al. 2006). For several decades, maize breeders have focused on short-term breeding. This has resulted in the development of a narrow genetic base for commercial maize hybrids (Darrah and Zuber 1986). A survey that was conducted in late 1970s and mid 1980s on inbred lines showed that some of the inbreds continued to contribute substantially to hybrids marketed in the United States. And the pedigrees of most hybrids are derivatives of 6–8 inbred lines (Darrah and Zuber 1986; James et al. 2002). In China, the parenthood of 91.6% hybrids consists of about 20 elite inbred lines (Li et al. 2002). With such a restrictive base, maize may not contain all the desirable and favourable alleles to maintain selection progress. Wuling mountain region covers Hunan, Hubei, Chongqing, and Guizhou provinces in China, where farmersaved maize landraces are still grown. The development of molecular markers provides a means of assessing genetic diversity at the DNA level (Reif et al. 2003). In particular, SSR markers are potentially useful for large-scale DNA fingerprinting of maize genotypes due to a high level of polymorphism detected (Smith et al. 1997), automated analysis systems (Sharon et al. 1997), and high accuracy and repeatability (Heckenberger et al. 2002). No attempts have been made so far to characterize maize landraces in Wuling mountain region using SSR markers. These original landraces represent a vast array of germplasm, which can be used in maize breeding for improving disease and pest

Bioinformatic prediction of microRNAs and their target genes in maize.

MicroRNAs (miRNAs) are an extensive class of tiny RNA molecules that regulate the expression of target genes by means of complementary base pair interactions. Identification of miRNAs and their target genes is essential to understand the regulation network of miRNAs in gene expression. With the method of bioinformatic computation, we used previously deposited miRNA sequences from Arabidopsis, rice, and other plant species to blast the databases of maize expressed sequence tags and genomic survey sequence that do not correspond to protein coding genes. A total of 11 novel miRNAs were identified from maize following a range of filtering criteria. All the potential miRNA precursors can be folded into the typical secondary structure of miRNA family, despite of variation in length and structure. Using these miRNAs sequences, we further blasted the databases of maize mRNAs and identified 26 target genes for seven of the eleven newly identified miRNAs. These genes encode twenty-six proteins involved in metabolism, signal transduction, transcriptional regulation, transmembrane transport, biostress, and abiostress responses, as well as chloroplast assembly. The identification of these novel miRNAs is a useful complement to the maize miRNA database.

A genetic study of the regeneration capacity of embryonic callus from the maize immature embryo culture

We carried out a study of regeneration capacities of embryonic callus from maize immature embryo culture with 144 different inbred lines of natural groups from different countries, and found that the regeneration capacity was affected by three factors: environment, genotype and the interaction between the environment and genotype. We found that green embryonic callus rate (GCR), embryonic callus differentiating rate (CDR) and the plantlet number of embryonic callus regeneration (CPN) have significant positive correlations with each other, and they all have significant negative correlations with embryonic callus browning rate (CBR). Moreover, embryonic callus cloning index for the first subculture (CCI1) and embryonic callus cloning index for the second subculture (CCI2) have a significant positive correlation with each other, and CCI2 is positively correlated with green GCR, and is negatively correlated with CBR. Embryonic callus rooting rate (CRR) is positively correlated with GCR, CDR and CPN to some degree. Furthermore, we calculated Broad-Sense Heritability of each trait, and uncovered that the heritability index of CCI1, CCI2 and CRR was lower, and the heritability index of others was higher. In addition, by using the Ward method for two-way cluster analysis, we found eleven inbred lines with high regenerating abilities, and the rooting situation of regenerating plantlet was excellent by rooting culture, which could be used as the elite inbred lines of the maize transgenic receptor.

QTL mapping of resistance to silk cut in maize.

Using 115 SSR markers and the F2 population consisting of 348 lines derived from the cross between maize (Zea mays L.) inbred lines R08 and Es40, a genetic linkage map associated with the resistance to silk cut was constructed. The genetic linkage map covered 2 178.6 cM of maize genome with an average mapping distance of 18.9 cM. Using the composite interval map- ping (CIM) method, 12 QTLs controlling the resistance to silk cut were detected on chromosomes 1, 2, 4, 5, and 7. These QTLs explained phenotypic variances ranging from 4.22% to 37.95%. Among them, two major QTLs on chromosomes 1 and 3, which explained more than 30% of phenotypic variances, had dominance effect, whereas, the other 10 QTLs had partial dominance effect or additive effect.