Introduction Of The Transposable Elements Ac/Ds Into Indica Rice Genome By Genetic Crossing

Rice (Oryza sativa L.) is one of the most important food crops in the world, and it is also a model plant system for genetics and functional genomics research in monocotyledons, especially in cereal species. Indica-type rice is the main resource of daily food for more than half the world's people, and indica rice varieties account for 80% of the cultivated rice. However, most, if not all, of indica-type rice varieties currently cultivated in China display less resistance to different biotic stresses, like diseases and pests, and abiotic stresses, like drought, cold, and salinity, and produce relatively poor quality of appearance, processing and nutrition, , which have greatly diminished their high yield potential. Creating and screening rice mutants related to potentially useful agronomic traits can not only develop novel germplasm for breeding indica-type rice varieties with improved stress resistance and high quality, but also provide abundant materials for indica rice genomics research. Although there have been established several technical platforms for insertional mutangenesis and gene tagging in japonica rice based on Ac/Ds transposable elements, similar mutant-generating tools have not yet been constructed in indica rice genome.In this study, conventional genetic cross-breeding techniques were exploited as a strategy to make cross combinations between japonica cultivar Dongjin Bye containing Ac/Ds, Ac or Ds and indica cultivars Ganzaoxian 37, Jiayu 948, Xianxiaonian, Xiangwanxian 11, Zhong'er ruanzhan, Zhongjian100, Zhongyouzao 81, Zunxian 3, Minghui 86, Yangdao 6, Yangxian 6547, Zhe 733, and Zhenhui 084, and perform inter-subspecific crosses. The hybrid progenies of F2 population and F1 derived from multiple cross were harvested, and used for Ac and Ds insertional identification by PCR analysis, thereafter, the progenies carrying both Ac and Ds elements were subjected to the molecular analysis for discriminating indica and japonica rice identity. The results indicated that genetic crosses between nine indica rice cultivars, including Minghui 86, and japonica Ac/Ds lines have resulted in fertile offspring , and among the progenies, plants containing Ac/Ds, Ac, and Ds accounted for 78.6%, 10.7%, and 1.5%, respectively. It was also found that both Ac and Ds might disappear during the vertical gene transfer from generation to generation. In order to discriminate the indica-japonica identity of hybrid rice by PCR assay, one pair of specific primers was screened out of 12 pairs of primers correponding to the all rice chromosomes, respectively. The results from PCR analysis showed that among hybrid prgenies, plants could be classified into indica, japonica, and indica-japonica rice, accounting for 35.5%, 15.6%, and 48.9%, respectively. This study also found that when genetic crosses were carried out using the same indica cultivar, such as Yangdao 6, Xiangwanxian 11, and Zhongjian100, as female parent in two generations, the progenies would be tested to be indica rice. It is suggested that inter-subspecific crosses of indica/japonica make it possible to introduce transposable genetic elements Ac/Ds into indica rice, and the gene tagging system be primarily established in indica rice.