Title : From microspore to embryo: how to get stressed and survive to tell
Microspores can be induced to change their developmental pathway and form haploid embryos in vitro. This process, known as microspore embryogenesis (ME), is generally induced by one or more stress treatments. ME can be easily induced in some species, e.g. Brassica napus, while other species are reclacitrant, including the model species arabidopsis and members of the Solanaceae. In B. napus, this change of developmental pathway is commonly induced by a heat stress. After the stress treatment, some microspores start to divide, other adopt a pollen-like development or arrest. Induced cells can either continue to form haploid embryos or arrest and die. We have observed that the fate of these dividing microspores is related to their stress response. Our data indicate that the induced microspores that do not follow further embryo development show endoplasmic reticulum (ER) accumulation (related to ER stress), high lytic activity, accumulation of starch and lipids, loss of cell adhesion. They become callus-like structures, and eventually undergo premature cell death. In embryo-like structures, all these processes are also present but at lower levels, which contributes to survival and conversion into differentiated embryos. Using cellular and molecular approaches we are studying the effect of several stress-related compounds in embryo yield and their role in the occurrence of the above mentioned features in different genotypes with different ME responses. Our aim is to link these cellular processes with stress response and cell fate in different genotypes, in an attempt to understand the underlying mechanisms, design ways to modulate these processes and eventually increase the number of cells committed to embryogenesis.