Seed germination plays a pivotal role during the life cycle of plants. As dry seeds imbibe water, the resumption of energy metabolism and cellular repair occur and miRNA-mediated gene expression regulation is involved in the reactivation events. This research was aimed at understanding the role of miRNA in the molecular control during seed imbibition process. Small RNA libraries constructed from dry and imbibed maize seed embryos were sequenced using the Illumina platform. Twenty-four conserved miRNA families were identified in both libraries. Sixteen of them showed significant expression differences between dry and imbibed seeds. Twelve miRNA families, miR156, miR159, miR164, miR166, miR167, miR168, miR169, miR172, miR319, miR393, miR394 and miR397, were significantly down-regulated; while four families, miR398, miR408, miR528 and miR529, were significantly up-regulated in imbibed seeds compared to that in dry seeds. Furthermore, putative novel maize miRNAs and their target genes were predicted. Target gene GO analysis was performed for novel miRNAs that were sequenced more than 50 times in the normalized libraries. The result showed that carbohydrate catabolic related genes were specifically enriched in the dry seed, while in imbibed seed target gene enrichment covered a broad range of functional categories including genes in amino acid biosynthesis, isomerase activity, ligase activity and others. The sequencing results were partially validated by quantitative RT-PCR for both conserved and novel miRNAs and the predicted target genes. Our data suggested that diverse and complex miRNAs are involved in the seed imbibition process. That miRNA are involved in plant hormone regulation may play important roles during the dry-imbibed seed transition.

Cross-incompatibility genes known as gametophyte factors (ga) are numerous in maize. Many popcorn strains carry these genes and cannot be fertilized by pollen of dent and flint maize strains although the reciprocal crosses are successful. A Chinese popcorn strain SDGa25 carries the strongest allele of Ga1 (Ga1-S) and the majority of Chinese dent and flint maize germplasm are incompatible with SDGa25. The incompatibility is due to pollen tube growth obstruction 2 h after pollination. The pollen tube is arrested in the silk segment 5.5 cm distal to the pollination area and never reaches the ovule. The Ga1-S carried by SDGa25 behaves as a single dominant gene. This gene was mapped between markers SD3 on BAC AC200747 0.827 cM apart on the telomere side and SD12 on BAC AC204382 0.709 cM apart on the centromere side. The genetic region mapped spanning the Ga1-S locus was estimated to be 1.5 cM in length and the physical distance is 2,056,343 bp on ctg156 based on the B73 RefGen_v2 sequence. Gametophyte factors influence gene flow direction and the strongest Ga1-S allele is useful for isolating one category of commercial varieties from another. The eight tightly linked markers to Ga1-S developed in this study would greatly improve marker-assisted introgression efficiency and the fine mapping would facilitate the isolation of the Ga1-S.

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873 RESEARCHM aize (Zea mays L.) is a cross-pollinating crop and the level of cross-fertilization among maize plants of neighboring fields is very high due to a heavy volume of pollen produced by the maize plant and factors such as wind and insects that facilitate pollen traveling. Many field experiments have been performed to study the cross-fertilization rate of maize (Henry et al. ABSTRACTPhenotyping of a mapping population is usually the bottleneck that limits the size of the mapping population and mapping resolution. A homogeneous population mapping approach was used for mapping maize (Zea mays L.) gametophytic factor 1 (ga1) that could completely eliminate phenotyping during the mapping process. The strong allele of maize ga1 (Ga1-S), from popcorn inbred line SDGa25, showed a 100% cross-incompatibility with the majority of Chinese dent and flint maize. A homogeneous mapping population was developed by crossing an (SDGa25/Jing66) F 1 male back to an SDGa25 female. During the pollination process, pollen grains of ga1 were completely excluded from fertilization, and a homogeneous BC 1 F 1 (SDGa25//SDGa25/Jing66) population was created in which only the Ga1-S/Ga1-S genotype existed, making phenotyping unnecessary. A total of 2245 individuals of this population were genotyped with SD9 and SD12 markers and 20 recombinants were identified. The Ga1-S locus was quickly delineated to a 100 Kb region between markers dCS1 and insertion deletion ID7 at position 9,491,422 and 9,591,946 bp based on the B73 RefGen_v2 sequence. By markerassisted selection, Ga1-S was introgressed into parental lines of an elite white waxy maize hybrid by six generations of backcrossing and one generation of selfing. The homozygous Ga1-S/Ga1-S hybrid showed full cross-incompatibility to ga1 maize. The Ga1-S allele could be used as a biological reproductive barrier in reducing crosspollination between different types of maize such as waxy and non-waxy, genetically modified (GM) and non-GM maize.

The effects of drying temperature and air velocity on the drying characteristics, color, bioactive compounds, rehydration ratio, and microstructure of Ophiopogonis Radix during hot air impingement drying (HAID) were explored in the current study. The experimental results showed that the drying temperature and air velocity had a significant impact on the drying characteristics and quality attributes of dried products except for the rehydration ratio. The drying time decreased from 720 to 240 min with the increase of drying temperature from 50 to 70 °C. Increasing the air velocity from 6 to 12 m/s enhanced the drying process of Ophiopogonis Radix, while the extension of air velocity to 15 m/s lowered the drying rate. The samples that were dried at a lower drying temperature obtained lower color difference. Properly increasing the drying temperature or air velocity could increase the total polysaccharide and flavonoid contents of dried products. Additionally, a back-propagation neural network (BPNN) model was developed to predict the moisture ratio of Ophiopogonis Radix during the drying process. The optimal BPNN with 3-11-1 topology were obtained to predict the moisture ratio of Ophiopogonis Radix during HAID and performed with an acceptable performance.