ELABORATION OF BODY PLAN AND PHASE CHANGE DURING DEVELOPMENT OF ACETABULARIA: How Is the Complex Architecture of a Giant Unicell Built?

Abstract

While uninucleate and unicellular, Acetabularia acetabulum establishes and maintains functionally and morphologically distinct body regions and executes phase changes like those in vascular plants. Centimeters tall at maturity, this species has allowed unusual experimental approaches. Amputations revealed fates of nucleate and enucleate portions from both wild type and mutants. Historically, graft chimeras between nucleate and enucleate portions suggested that morphological instructions were supplied by the nucleus but resided in the cytoplasm and could be expressed interspecifically. Recently, graft chimeras enabled rescue of mutants arrested in vegetative phase. Since the 1930s, when Acetabularia provided the first evidence for the existence of mRNAs, a dogma has arisen that it uses long-lived mRNAs to effect morphogenesis. While the evidence favors translational control, the postulated mRNAs have not been identified, and the mechanism of morphogenesis remains unknown. Amenable to biochemistry, physiology, and both classical and molecular genetics, Acetabularia may contribute yet new insights into plant development and morphogenesis.

Green Algae and the Origins of Multicellularity in the Plant Kingdom

“…The most well-known species of this type are in the genus Acetabularia (an ulvophyte) that is famous for transplantation experiments demonstrating nuclear control over cell morphology (Mandoli 1998;Mine et al 2008). …”

Phylogeny and Molecular Evolution of the Green Algae

“…Transplant experiments with the giant-celled Acetabularia, conducted by Joachim Hämmerling, demonstrated that the nucleus of a cell contains the genetic information that directs cellular development, and postulated the existence of messenger RNA before its structure was determined (Hämmerling, 1953). Acetabularia, along with other giant-celled green algae (Valonia, Chara and Nitella), has also served as an experimental organism for electro-physiological research and studies of cell morphogenesis (Menzel, 1994;Mandoli, 1998;Shepherd et al, 2004;Bisson et al, 2006;Mine et al, 2008). The charophyte Mougeotia played a key role in outlining the role of phytochrome in plant development (Winands & Wagner, 1996).…”

Paths toward Algal Genomics

“…Plastid and nuclear genomes of C. reinhardtii are readily transformed (Debuchy et al, 1989;Kindle et al, 1989;Diener et al, 1990;Mayfield and Kindle, 1990;Shimogawara et al, 1998) using any of a number of different selectable markers (Debuchy et al, 1989;Fernandez et al, 1989;Kindle, 1990;GoldschmidtClermont, 1991;Nelson et al, 1994;Stevens et al, 1996;Lumbreras et al, 1998;Auchincloss et al, 1999;Kovar et al, 2002). Plasmid, cosmid, and bacterial artificial chromosome libraries (Purton and Rochaix, 1994;Zhang et al, 1994;Lefebvre and Silflow, 1999) al., 1998;Wykoff et al, 1998) or E. coli Palombella and Dutcher, 1998) mutant strains. Methods have been developed for generating tagged mutant alleles (Tam and Lefebvre, 1993;Davies et al, 1994Davies et al, , 1996Smith and Lefebvre, 1996;Koutoulis et al, 1997;Smith and Lefebvre, 1997;Zhang and Lefebvre, 1997;Asleson and Lefebvre, 1998;Davies et al, 1999;Wykoff et al, 1999), and alleles not tagged can be isolated by map-based cloning (Vysotskaia et al, 2001;Kathir et al, 2003).…”

“…It is an organism that can readily be used to study those transcripts generated in the nucleus (which is located in the cell rhizoid) and transmitted/accumulated in more distal locations of the cell where they control biological processes. Developmental studies concerning Acetabularia have recently been discussed (Mandoli, 1998), and a comparison of cDNAs from the juvenile and adult stage has been initiated (Henry et al, 2004). An equally interesting organism is Caulerpa.…”

“…The root and leaflike structures of this organism are supported by a stem-like structure, and even though it is a single cell, it may extend for well over a meter (Graham and Wilcox, 2000). This alga does not produce specialized reproductive cells (unlike Acetabularia, which produces a reproductive cap-like structure; see Mandoli, 1998) but directs all of its vegetative resources into the generation of progeny. Furthermore, there are Caulerpa species that respond to gravity like flowering plants and that synthesize and respond to plant hormones.…”