Previous studies have revealed the miR164 family and the miR164-targeted NAC transcription factor genes in rice (Oryza sativa) and Arabidopsis that play versatile roles in developmental processes and stress responses.  In wheat (Triticum aestivum L.), we found nine genetic loci of tae-miR164 (tae-MIR164 a to i) producing two mature sequences that down-regulate the expression of three newly identified target genes of TaNACs (TaNAC1, TaNAC11, and TaNAC14) by the cleavage of the respective mRNAs.  Overexpression of tae-miR164 or one of its target genes (TaNAC14) demonstrated that the miR164-TaNAC14 module greatly affects root growth and development and stress (drought and salinity) tolerance in wheat seedlings, and TaNAC14 promotes root growth and development in wheat seedlings and enhances drought tolerance, while tae-miR164 inhibits root development and reduces drought and salinity tolerance by down-regulating the expression of TaNAC14.  These findings identify the miR164-TaNAC14 module as well as other tae-miR164-regulated genes which can serve as new genetic resources for stress-resistance wheat breeding.

MicroRNAs (miRNAs) are small (ca. 20–24 nucleotides) non-coding RNAs that have recently been recognized as key post-transcriptional modulators of gene expression; and they are involved in many biological processes in plants, such as root growth and development.  The miRNAs regulate root elongation, lateral root (LR) formation and adventitious root (AR) development in response to hormone signaling, nutrient uptake and biotic/abiotic stress.  This review provides multiple perspectives on the involvement of miRNAs in regulating root growth and development in plants.  We also discuss several crucial mechanisms of miRNAs, their relationships with transcription factors and the target gene-mediated hormone signaling interactions in the regulation of root growth and development.

Maedi-visna virus (MVV) is an ovine lentivirus that is widespread in many countries worldwide. Both clinical and subclinical MVV infections cause substantial economic losses. MVV infection in live sheep is usually diagnosed serologically, with antibody-positive sheep being regarded as infected. There have been few reports of maedi-visna in China, with no detailed epidemic analysis of MVV infection in ovine herds. In order to investigate the seroprevalence and spatial distribution of maedi-visna among ovine flocks in China, a total of 672 serum samples were collected from different ovine flocks in 12 regions (provinces, autonomous regions or municipalities) of China in 2011, and serum antibody levels were determined using a commercial ELISA Kit. This study represents the first investigation of the seroepidemiology of maedi-visna in China, indicating a circulation of MMV among sheep.

Selection for phosphorus (P)-efficient genotypes and investigation of physiological mechanisms for P-use efficiency in maize has mainly been conducted at the seedling stage under controlled greenhouse conditions. Few studies have analyzed characteristics of plant growth and yield formation in response to low-P stress over the whole growth period under field conditions. In the present study, two maize inbred lines with contrasting yield performances under low-P stress in the field were used to compare plant growth, P uptake and translocation, and yield formation. Phosphorus accumulation in the P-efficient line 154 was similar to that of line 153 under high-P. Under low-P, however, P uptake in line 154 was three times greater than that in line 153. Correspondingly, P-efficient line 154 had a significantly higher yield than P-inefficient line 153 under low-P conditions (Olsen-P=1.60 mg kg-1), but not under high-P conditions (Olsen-P=14.98 mg kg-1). The yield difference was mainly due to differences in the number of ears per m2, that is, P-efficient line 154 formed many more ears under low-P conditions than P-inefficient line 153. Ear abortion rate was 53% in the P-inefficient line 153, while in line 154, it was only 30%. Low-P stress reduced leaf appearance, and delayed anthesis and the silking stage, but increased the anthesis-silking interval (ASI) to a similar extent in both lines. The maximum leaf area per plant at silking stage was higher in P-efficient line 154 than in P-inefficient line 153 under both P conditions. It is concluded that low-P stress causes intense intraspecific competition for limited P resources in the field condition which gives rise to plant-toplant non-uniformity, resulting in a higher proportion of barren plants. As soon as an ear was formed in the plant, P in the plant is efficiently reutilized for kernel development.

Oryza officinalis is one of the important wild species in the tertiary gene pool of Oryza sativa. It has a number of elite genes for rice breeding in resistance or tolerance. However, breeding barriers are so serious that the gene transfer is much difficult by sexual cross method between O. sativa and O. officinalis. Characteristics of the breeding barriers were systemically studied in this paper. When both the diploid (AA, 2n=2x=24) and autotetraploid (AAAA, 2n=4x=48) cultivated rice were crossed as maternal parents with O. officinalis (CC, 2n=2x=24), none F1 hybrid seeds were obtained. The young hybrid ovaries aborted at 13-16 d after pollinations (DAP). By rescuing hybrid embryos, in vitro F1 plantlets were obtained in 2x×2x combinations with the crossabilities lower than 0.5%. Lower rates of double-fertilization and abnormal development of hybrid embryo and endosperm were mainly observed in both combinations of 2x×2x and 4x×2x. Free endosperm nuclei in hybrid degenerated early at 1 DAP in a large scale. Almost no normal endosperm cells formed at 3 DAP. Development of a lot of embryos ceased at globular- or pear-shaped stage as well as some degenerated gradually. The hybrid plantlets were both male and female sterility. Due to the abnormal development, a diversity of abnormal embryo sacs formed in hybrids, and hybrid pollen grains were typically abortive. It showed that conflicts of genome A and C in hybrid induced abnormal meioses of meiocytes.