This document summarizes a presentation on the giant single-celled alga Caulerpa taxifolia. It discusses how C. taxifolia exhibits intracellular patterns of gene expression that coincide with pseudo-organs, similar to the molecular patterning seen in land plant organs. This raises questions about potential molecular homology between algal pseudo-organs and plant organs. The presentation also examines outstanding questions about intracellular transport, nuclear equivalence, and the potential for a soma-germline divide in these giant coenocytes. Overall, it explores how complex morphologies can arise without multicellularity through intracellular gene regulation and signaling.

1. Plant architecture
without multicellularity:
An intracellular
transcriptomic atlas of a
giant, single-celled alga
Dan Chitwood
Donald Danforth Plant Science Center
74th Society for Developmental Biology
July 11, 2015

2. Independent origins of multicellularity

3. Independent origins of multicellularity
Opisthokonts
Streptophytes
Viridiplantae
Plantae
Chlorophytes
Rhodophytes
Algae
(polyphyletic)
M Abedin & N King (2010)
Trends in Cell Biology

4. Independent origins of multicellularity
Opisthokonts
Streptophytes
Viridiplantae
Plantae
Chlorophytes
Rhodophytes
Algae
(polyphyletic)
M Abedin & N King (2010)
Trends in Cell Biology

5. Independent origins of multicellularity
Opisthokonts
Streptophytes
Viridiplantae
Plantae
Chlorophytes
Rhodophytes
Algae
(polyphyletic)
M Abedin & N King (2010)
Trends in Cell Biology

6. Independent origins of multicellularity
Opisthokonts
Streptophytes
Viridiplantae
Plantae
Chlorophytes
Rhodophytes
Algae
(polyphyletic)

7. Independent origins of multicellularity
Opisthokonts
Streptophytes
Viridiplantae
Plantae
Chlorophytes
Rhodophytes
Algae
(polyphyletic)

8. Independent origins of multicellularity
Opisthokonts
Streptophytes
Viridiplantae
Plantae
Chlorophytes
Rhodophytes
Algae
(polyphyletic)

9. Macroscopic morphological complexity:
plant architecture without multicellularity
V Coneva & D Chitwood (2015)
Front Plant Sci

10. Macroscopic morphological complexity:
plant architecture without multicellularity
Ernst Haeckel, Wikipedia,
Wikimedia commons

11. Cell vs. Organismal Theory:
Plant development ≠ Animal development
Kaplan and Hagemann (1991)
BioScience

12. Cell vs. Organismal Theory:
Plant development ≠ Animal development
1) Plasmodesmata, symplasm
Kaplan and Hagemann (1991)
BioScience
Cilia and Jackson (2004)
Curr Opin in Cell Biol

13. Kaplan and Hagemann (1991)
BioScience
Cell vs. Organismal Theory:
Plant development ≠ Animal development
1) Plasmodesmata, symplasm
2) Phragmoplasts

14. Kaplan and Hagemann (1991)
BioScience
Cell vs. Organismal Theory:
Plant development ≠ Animal development
1) Plasmodesmata, symplasm
2) Phragmoplasts
3) Cell lineage patterns

15. Kaplan and Hagemann (1991)
BioScience
Cell vs. Organismal Theory:
Plant development ≠ Animal development
1) Plasmodesmata, symplasm
2) Phragmoplasts
3) Cell lineage patterns

16. Brukhin, Curtis, Grossniklaus (2005)
Current Science
Cell vs. Organismal Theory:
Plant development ≠ Animal development
1) Plasmodesmata, symplasm
2) Phragmoplasts
3) Cell lineage patterns
4) Coenocytic female gametophyte

17. Kaplan and Hagemann (1991)
BioScience
Cell vs. Organismal Theory:
Plant development ≠ Animal development
1) Plasmodesmata, symplasm
2) Phragmoplasts
3) Cell lineage patterns
4) Coenocytic female gametophyte
Conclusion: there is as much evidence to view
morphologically complex plants as coenocytes as
there is to consider them multicellular (at least in the
same sense as animals)

18. An intracellular transcriptomic atlas of the
giant coenocyte Caulerpa taxifolia
Ranjan et al. (2015)
PLOS Genetics

19. An intracellular transcriptomic atlas of the
giant coenocyte Caulerpa taxifolia
Why Caulerpa taxifolia?
1) Debatably world’s largest single-
celled organism
Ranjan et al. (2015)
PLOS Genetics

20. An intracellular transcriptomic atlas of the
giant coenocyte Caulerpa taxifolia
Why Caulerpa taxifolia?
1) Debatably world’s largest single-
celled organism
2) Can regenerate from any fragment
Ranjan et al. (2015)
PLOS Genetics

21. An intracellular transcriptomic atlas of the
giant coenocyte Caulerpa taxifolia
Why Caulerpa taxifolia?
1) Debatably world’s largest single-
celled organism
2) Can regenerate from any fragment
3) “Killer algae”—invasive
Ranjan et al. (2015)
PLOS Genetics

22. An intracellular transcriptomic atlas of the
giant coenocyte Caulerpa taxifolia
Why Caulerpa taxifolia?
1) Debatably world’s largest single-
celled organism
2) Can regenerate from any fragment
3) “Killer algae”—invasive
4) Endosymbiotic bacteria
Ranjan et al. (2015)
PLOS Genetics

23. An intracellular transcriptomic atlas of the
giant coenocyte Caulerpa taxifolia
Why Caulerpa taxifolia?
1) Debatably world’s largest single-
celled organism
2) Can regenerate from any fragment
3) “Killer algae”—invasive
4) Endosymbiotic bacteria
5) Convergent morphology with land
plants
Ranjan et al. (2015)
PLOS Genetics

24. An intracellular transcriptomic atlas of the
giant coenocyte Caulerpa taxifolia
Ranjan et al. (2015)
PLOS Genetics

25. A “wave” of apical-basal
gene expression
Ranjan et al. (2015)
PLOS Genetics

26. A “wave” of apical-basal
gene expression
Ranjan et al. (2015)
PLOS Genetics

27. A “wave” of apical-basal
gene expression
Ranjan et al. (2015)
PLOS Genetics

28. A “wave” of apical-basal
gene expression
Ranjan et al. (2015)
PLOS Genetics

29. A “wave” of apical-basal
gene expression
Ranjan et al. (2015)
PLOS Genetics

30. A “wave” of apical-basal
gene expression
Ranjan et al. (2015)
PLOS Genetics

31. A “wave” of apical-basal
gene expression
Ranjan et al. (2015)
PLOS Genetics

32. A “wave” of apical-basal
gene expression
Ranjan et al. (2015)
PLOS Genetics

33. A “wave” of apical-basal
gene expression
Ranjan et al. (2015)
PLOS Genetics

34. Intracellular patterns
of gene expression
coincide with pseudo-
organs
Ranjan et al. (2015)
PLOS Genetics

35. Intracellular patterns
of gene expression
coincide with pseudo-
organs
Ranjan et al. (2015)
PLOS Genetics

36. Molecular homology between land plant
organs and algal pseudo-organs?

37. Molecular homology between land plant
organs and algal pseudo-organs?
Ranjan et al. (2015)
PLOS Genetics

38. Molecular homology between land plant
organs and algal pseudo-organs?
Ranjan et al. (2015)
PLOS Genetics
??
D Reinhardt

39. Molecular homology between land plant
organs and algal pseudo-organs?
Ranjan et al. (2015)
PLOS Genetics
?

40. Molecular homology between land plant
organs and algal pseudo-organs?
Ranjan et al. (2015)
PLOS Genetics

41. Molecular homology between land plant
organs and algal pseudo-organs?
Ranjan et al. (2015)
PLOS Genetics
D Reinhardt

42. More questions …

43. More questions …
V Coneva & D Chitwood (2015)
Front Plant Sci
Future directions
1) Small RNA movement
2) mRNA movement

44. More questions …
V Coneva & D Chitwood (2015)
Front Plant Sci
Future directions
1) Small RNA movement
2) mRNA movement

45. More questions …
V Coneva & D Chitwood (2015)
Front Plant Sci
Future directions
1) Small RNA movement
2) mRNA movement
3) Are nuclei functionally
equivalent?
4) Soma-germline divide?

46. More questions …
V Coneva & D Chitwood (2015)
Front Plant Sci
Future directions
1) Small RNA movement
2) mRNA movement
3) Are nuclei functionally
equivalent?
4) Soma-germline divide?
5) Genome sequencing

47. More questions …
V Coneva & D Chitwood (2015)
Front Plant Sci
Future directions
1) Small RNA movement
2) mRNA movement
3) Are nuclei functionally
equivalent?
4) Soma-germline divide?
5) Genome sequencing
6) Intracellular
microbiome

48. Thanks!
Chitwood lab
Viktoriya Coneva
Margaret Frank
Sinha Lab
Aashish Ranjan
Brad Townsley
Yasunori Ichihashi
Funding
Gordon & Betty
Moore Foundation
Life Sciences Research
Fellowship