Growth and developmental analysis of T1 generation from BpAP1 transgenic birch.

Woody plants are characterized by long developing period and high heterozygosity. It is important to shorten the life cycle of trees in tree breeding. APETALA1 (AP1) is a member of MADS-box gene family involved in flower development in plants. Overexpression of AP1 genes induces early flowering in transgenic plants. In order to investigate the genetic stability and regularity of foreign BpAP1 gene in BpAP1 transgenic birch, we generated T1 generation seedlings using three 35S∷BpAP1 transgenic plants and one wild-type plant as male parents, and three wild-type birch, Betula platyphylla × Betula pendula, as female parents. The growth, development and flowering characteristics of the T1 generation seedlings were analyzed. The results indicated that the foreign BpAP1 slightly influenced the pollen vitality of transgenic plants. About 36%-58% of T1 generation inherited the foreign BpAP1 gene from their parents. Chi-square test of BpAP1 gene segregation ratios revealed that BpAP1 was inherited in accordance with Mendelian inheritance. T1 generation seedlings carrying BpAP1 gene inherited the characteristics of early flowering and dwarfism from their male parent. The average heights of 1-and 2-year-old T1 generation seedlings carrying BpAP1 gene were significantly shorter than the progeny from hybridization of wild-type birch with the percentages of 44.19% and 18.92%, respectively. The phenotypes of T1 generation birch carrying foreign BpAP1 gene were quite different from the ones that were lack of foreign BpAP1 gene. According to the different phenotypes, we can infer whether the T1 generation seedlings carry BpAP1 gene or not. Our study proved that the exogenous AP1 gene can be stably inherited by sexual reproduction, and the acquired transgenic birch lines exhibited accelerated flowering time and a shortened juvenile phase, indicating that it can be used as parent materials for genetic studies on birch traits.