Xiang Fengning

Effect of UV dosage on somatic hybridization between common wheat (Triticum aestivum L.) and Avena sativa L.

Protoplasts of Avena sativa L. (A) irradiated with ultraviolet light (UV) at an intensity of 300 μW/cm2 for 0 (symmetric fusion), 30 s, 1 min, 2 min, 3 min, 5 min, respectively were fused by the PEG method with protoplasts of two cultivars of wheat (cv. Jinan 177 or cv. Hesheng 3). Two different sources of material were used for isolation of protoplasts of Jinan 177. Type one (T1) originated from long-term subcultured suspensions which could not be regenerated to plants, while the other (T2) derived from embryogenic calli was capable of regeneration. Protoplasts of cv. Hesheng 3 (T3) also originated from embryogenic calli possessing high regeneration capacity. Regenerated clones were produced in all fusion combinations, but only those from combinations IB and IC (irradiating A. sativa for 1 and 2 min) differentiated to albinos. The clones were recognized as somatic hybrids in nature by cytological, isozyme, RAPD and 5S rDNA spacer sequence analysis. Genomic in situ hybridization (GISH) of somatic hybrid clones at mitosis always revealed the presence of recombined and intact A. sativa chromosomes in the cells. The number of intact chromosomes of donor A. sativa decreased, while the chromosome fragments translocated or inserted to wheat chromosome increased as the dosage of UV enhanced.

Asymmetric somatic hybridization between haploid common wheat and UV-irradiated Haynaldia villosa

UV irradiated protoplasts from young embryo derived calli of Haynaldia villosa were fused with protoplasts originated from anther derived calli of Triticum aestivum cv. 24-2 by the PEG method. Regenerated calli from fusion cells were obtained but none of them differentiated into plants. The cell clones that formed early were examined for their hybrid nature, chromosome counting and isozyme analysis suggested that they were nuclear hybrid. Further unequivocal confirmation was accomplished using the technique of in situ hybridization (ISH) and RAPD analysis, which facilitated the identification of the hybrid nature in fusion products. The results revealed that UV might have played an important role in breaking donor chromosomes and ensuring the introduction of alien chromatin into the recipient via asymmetric hybridization. The failure of plant regeneration of the somatic hybrids was discussed and further investigations are being conducted.

Auxin response factors and plant growth and development

An important aspect of studies on auxin is auxin response factors (ARFs), which activate or repress the auxin response genes by binding to auxin response elements (AuxREs) on their promoters. In this review, we focused on molecular biological advances of plant ARF families, and discussed ARF structures, regulation of ARF gene expression, the roles of ARFs in regulating the development of plants and in signal transduction and the mechanisms involved in the target gene regulation by ARFs. The phylogenetic relationships of ARFs in plants are close and most of them have 4 domains. ARFs are expressed in various tissues. Their expressions are regulated at both transcriptional and post-transcriptional levels. They play important roles in the interactions between auxin and other hormones.