Guan-Zheng Qu

Overexpression of a MADS-Box Gene from Birch (Betula platyphylla) Promotes Flowering and Enhances Chloroplast Development in Transgenic Tobacco

In this study, a MADS-box gene (BpMADS), which is an ortholog of AP1 from Arabidopsis, was isolated from birch (Betula platyphylla). Transgenic Arabidopsis containing a BpMADS promoter::GUS construct was produced, which exhibited strong GUS staining in sepal tissues. Ectopic expression of BpMADS significantly enhanced the flowering of tobacco (35S::BpMADS). In addition, the chloroplasts of transgenic tobacco exhibited much higher growth and division rates, as well rates of photosynthesis, than wild-type. A grafting experiment demonstrated that the flowering time of the scion was not affected by stock that overexpressed BpMADS. In addition, the overexpression of BpMADS resulted in the upregulation of some flowering-related genes in tobacco.

Overexpression of two PsnAP1 genes from Populus simonii × P. nigra causes early flowering in transgenic tobacco and Arabidopsis.

In Arabidopsis, AP1 is a floral meristem identity gene and plays an important role in floral organ development. In this study, PsnAP1-1 and PsnAP1-2 were isolated from the male reproductive buds of poplar (Populus simonii × P. nigra), which are the orthologs of AP1 in Arabidopsis, by sequence analysis. Northern blot and qRT-PCR analysis showed that PsnAP1-1 and PsnAP1-2 exhibited high expression level in early inflorescence development of poplar. Subcellular localization showed the PsnAP1-1 and PsnAP1-2 proteins are localized in the nucleus. Overexpression of PsnAP1-1 and PsnAP1-2 in tobacco under the control of a CaMV 35S promoter significantly enhanced early flowering. These transgenic plants also showed much earlier stem initiation and higher rates of photosynthesis than did wild-type tobacco. qRT-PCR analysis further indicated that overexpression of PsnAP1-1 and PsnAP1-2 resulted in up-regulation of genes related to flowering, such as NtMADS4, NtMADS5 and NtMADS11. Overexpression of PsnAP1-1 and PsnAP1-2 in Arabidopsis also induced early flowering, but did not complement the ap1-10 floral morphology to any noticeable extent. This study indicates that PsnAP1-1 and PsnAP1-2 play a role in floral transition of poplar.

Effect of Hormones on Tumor Formation in Tobacco Hybrids

Genetic tumors can develop on certain tobacco hybrid plant spontaneously. In this study, exogenous hormones were applied on the tumorous tobacco hybrid seedlings (N. glauca × N. langsdorffii), and the data showed that N6-benzyladenine (BA) enhanced the tumor formation under both tissue culture and field conditions, and NAA and ABA inhibited tumor formation under tissue culture condition, whereas ABA accelerated the tumor formation under field condition. Furthermore, Northern analysis indicated that tumor tissue exhibited high level of CycD expression compared with normal tissues, implying abnormal cell cycle of tumor cells. The differential display reverse transcription PCR (DDRT PCR) results indicated some genes may be involved in tumor formation.

Variation Analysis of Physiological Traits in Betula platyphylla Overexpressing TaLEA-ThbZIP Gene under Salt Stress

The aim of this study was to determine whether transgenic birch (Betula platyphylla) ectopic overexpressing a late embryogenesis abundant (LEA) gene and a basic leucine zipper (bZIP) gene from the salt-tolerant genus Tamarix (salt cedar) show increased tolerance to salt (NaCl) stress. Co-transfer of TaLEA and ThbZIP in birch under the control of two independent CaMV 35S promoters significantly enhanced salt stress. PCR and northern blot analyses indicated that the two genes were ectopically overexpressed in several dual-gene transgenic birch lines. We compared the effects of salt stress among three transgenic birch lines (L-4, L-5, and L-8) and wild type (WT). In all lines, the net photosynthesis values were higher before salt stress treatment than afterwards. After the salt stress treatment, the transgenic lines L-4 and L-8 showed higher values for photosynthetic traits, chlorophyll fluorescence, peroxidase and superoxide dismutase activities, and lower malondialdehyde and Na+ contents, compared with those in WT and L-5. These different responses to salt stress suggested that the transcriptional level of the TaLEA and ThbZIP genes differed among the transgenic lines, resulting in a variety of genetic and phenotypic effects. The results of this research can provide a theoretical basis for the genetic engineering of salt-tolerant trees.

Morphological and genetic characteristics of genetic tumor in Nicotiana glauca

It is well understood that genetic tumors develop in certain interspecific Nicotiana hybrids. Nicotiana species are divided into “plus” and “minus” groups and crosses between “plus” and “minus” species give rise to tumorous hybrids. However, it has been proposed that parents and hybrids derived from crosses among members within the same group do not produce tumors. In this study, genetic tumors were only obtained in Nicotiana glauca, which exhibited tumor features similar to those of N. glauca × N. langsdorffii. Our results suggest that genetic factors may control tumor formation independent of tumor induction dependent on the specific interspecific cross. Genetic tumor formation exhibited high B-type and D-type cyclin expression levels, indicating tumor cells are characterized by an uncontrolled cell cycle.