title: Plasticity in Cell Division Patterns and Auxin Transport Dependency during in Vitro Embryogenesis in Brassica napus.
abstract: In Arabidopsis thaliana, zygotic embryo divisions are highly regular, but it is not clear how embryo patterning is established in species or culture systems with irregular cell divisions. We investigated this using the Brassica napus microspore embryogenesis system, where the male gametophyte is reprogrammed in vitro to form haploid embryos in the absence of exogenous growth regulators. Microspore embryos are formed via two pathways: a zygotic-like pathway, characterized by initial suspensor formation followed by embryo proper formation from the distal cell of the suspensor, and a pathway characterized by initially unorganized embryos lacking a suspensor. Using embryo fate and auxin markers, we show that the zygotic-like pathway requires polar auxin transport for embryo proper specification from the suspensor, while the suspensorless pathway is polar auxin transport independent and marked by an initial auxin maximum, suggesting early embryo proper establishment in the absence of a basal suspensor. Polarity establishment in this suspensorless pathway was triggered and guided by rupture of the pollen exine. Irregular division patterns did not affect cell fate establishment in either pathway. These results confirm the importance of the suspensor and suspensor-driven auxin transport in patterning, but also uncover a mechanism where cell patterning is less regular and independent of auxin transport.
authors.affiliation: Plant Research International, 6700 AP Wageningen, The Netherlands.
authors.forename: Mercedes
authors.initials: M
authors.lastname: Soriano
authors.affiliation: Plant Research International, 6700 AP Wageningen, The Netherlands.
authors.forename: Hui
authors.initials: H
authors.lastname: Li
authors.affiliation: Université de Reims Champagne-Ardenne, Unité de Recherche Vignes et Vins de Champagne-EA 4707, Laboratoire de Stress, Défenses et Reproduction des Plantes, Moulin de la Housse, 51687 REIMS Cedex 2, France.
authors.forename: Cédric
authors.initials: C
authors.lastname: Jacquard
authors.affiliation: Plant Research International, 6700 AP Wageningen, The Netherlands Laboratory for Molecular Biology, Wageningen University, 6708 PB, Wageningen, The Netherlands.
authors.forename: Gerco C
authors.initials: GC
authors.lastname: Angenent
authors.affiliation: Plant Biotechnology Institute, National Research Council of Canada, Saskatoon S7N 0W9, Canada.
authors.forename: Joan
authors.initials: J
authors.lastname: Krochko
authors.affiliation: Molecular and Developmental Genetics, Institute Biology Leiden, Leiden University, 2333 BE Leiden, The Netherlands.
authors.forename: Remko
authors.initials: R
authors.lastname: Offringa
authors.affiliation: Plant Research International, 6700 AP Wageningen, The Netherlands kim.boutilier@wur.nl.
authors.forename: Kim
authors.initials: K
authors.lastname: Boutilier