Double-seedlings and embryo-free seeds generated by genetic engineering

Area of Science:

• Plant Biotechnology
• Reproductive Biology
• Genetics

Background:

• Apomixis, asexual reproduction through seeds, can preserve hybrid vigor (heterosis) in F1 hybrids.
• Developing apomictic hybrid rice is crucial for efficient hybrid seed production and maintaining desirable traits.
• Current methods for hybrid rice development rely on cross-pollination, which can be labor-intensive.

Purpose of the Study:

• To engineer a strategy for inducing apomictic reproduction in hybrid rice via adventitious embryos.
• To investigate the genetic control of embryo development and endosperm formation in rice.
• To explore the potential for clonal propagation of hybrid rice through synthetic apomixis.

Main Methods:

• Simultaneous transformation of rice with two T-DNAs carrying specific genes: an embryogenesis gene (AtWUS), a ribonuclease gene (Barnase), an inactivation gene (ZmAA1), and a suppressor gene (Barstar).
• Utilized ovule-specific, egg cell-specific, and pollen-specific promoters to control gene expression.
• Confirmed ploidy levels and zygotic/gametic origins of seedlings using whole-genome sequencing and flow cytometry.

Main Results:

• Observed 'double-seedlings' in transgenic lines: one heterozygous diploid (zygotic) and one homozygous haploid (gametic).
• Achieved embryo-free seeds at frequencies of 2.6–3.8% in the T1 generation and 0.75–3% in the T2 generation.
• Did not obtain adventitious embryos, but observed phenomena suggest endosperm development is independent of fertilization.

Conclusions:

• The study provides evidence supporting the autonomous development of the endosperm in rice.
• The observed double-seedlings and embryo-free seeds offer insights into inducing haploid embryos.
• This research lays theoretical groundwork for successful clonal propagation using synthetic apomixis in rice.