Mechanistic dissection of plant embryo initiation

Land plants can reproduce sexually by developing an embryo from a fertilized egg cell, the zygote. After fertilization, the zygote undergoes several rounds of controlled cell divisions to generate a mature embryo. However, embryo formation can also be induced in a variety of other cell types in many plant species. These non-zygotic embryos go through analogous developmental phases and are morphologically similar to the zygotic embryo. Despite its fundamental importance and enormous application potential, the mechanisms that alter cell fate from non-embryonic to embryonic are elusive. In the past decades, a variety of different model systems have been used to identify regulators of embryo induction, but it is unclear if these act in a common network. We recently found that inhibition of auxin response in the extra-embryonic suspensor cells cell-autonomously and predictably triggers a switch towards embryo identity. In my thesis I have used the suspensor-derived embryogenesis as a uniform model system to study the crucial first reprogramming step of embryo initiation process.

Through genome-wide transcriptional profiling upon local (suspensor-specific) auxin response inhibition (Chapter 2) and through testing the ability of fifteen known embryogenesis inducers to promote embryo formation in suspensor cells (Chapter 3), we suggest that suspensor to embryo transformation requires a defined set of genetic regulators. The results obtained in my thesis provide essential tools and basis for further research and are a step forward to understanding the first step of embryo initiation process and to unravel the mystery of totipotency in plants.