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Abstract:
Zygote development serves as a pivotal point in the life cycle, connecting the gametophytic and sporophytic life stages and playing a crucial role in the recruitment of the next generation of seaweeds. Broadcast spawning brown algae are excellent models for studying processes during the life cycle transition, asymmetric cell division, and attachment because of their synchronous development free from maternal tissue. In the oogamous brown alga Dictyota dichotoma, early development has been described. The sporophytic developmental program is rapidly activated following fertilization, unlike in animal systems. After 1 to 2 minutes of rapid elongation, the zygote undergoes asymmetric cell division, establishing the apical-basal pattern, with the elongated zygote developing into the rhizoid responsible for seaweed recruitment. In addition, basal cell fate differentiation in Dictyota shows a remarkable degree of phenotypic plasticity and may be postponed under the control of an endogenous volatile compound. The ability to control asymmetric cell division versus symmetric cell division enables the comparison of a polarized zygote with an unpolarized zygote in the same developmental context. Using cell polarization assays combined with transcriptomics, we describe the phenotypic modulation of asymmetric division into a symmetric cell division.
