RC17. Phylogenetic and physicochemical constraints on the evolution of function in algae and plants

9th June 2009, at Macquarie University, Sydney.	SPEAKERS INCLUDE John Raven - Dundee U (Scotland), plant physiology John Beardall - Monash U, algal and plant ecophysiology Jason Bragg - MIT (USA), functional genomics John Evans - ANU, Canberra, plant ecophysiology Zoe Finkel - Mt Allison U (Canada), algal biogeochemistry and allometry Charles Knight - California Polytechnic State U (USA), genome size and functional ecology

On Tuesday 9th June there will be an intensive 1-day research course offered, open to interested researchers and ECR and HDR.

The purpose of the remainder of the week for working group participants will be to analyse the extent to which variation in genome size and rDNA copy number accounts for variation in (1) cell size and (2) maximum cell division rate, and how much of the variance in cell size and growth rate these two factors do not account for.

Background
Cell volume varies over a range of 1015-fold among photosynthetic organisms, with a range of 1012-fold in the cytoplasmic volume. The range is larger for unicellular organisms (acellular rather than unicellular for the larger representatives) than for component cells in multicellular organisms. There is a general positive correlation within higher taxa between cytoplasm volume per cell and the cell DNA content resulting from variations in DNA C-value, endopolyploidy, polyteny and coenocytic organisation. There is also a general negative correlation in many higher taxa between cytoplasmic volume and the maximum rate of cell division. Similar correlations with cytoplasm size are found for rDNA copy number, but there is also a positive correlation of rDNA copy number with the maximum rate of cell division. The working group will produce papers relating to two aspects of these inter-relations.

One objective of WG55 is to analyse the extent to which variation in genome size and rDNA copy number accounts for variation in (1) cell size and in (2) maximum cell division rate, and how much of the variance in cell size and growth rate these two factors do not account for. A subsidiary question is the extent to which the acellular life-form in benthic organisms imposes constraints in terms of achievable growth rate and economy in the use of resources compared to multicellular organisms of the same size growing in the same habitat. This subsidiary question was considered for unicellular, colonial and multicellular phytoplankton in the recent Tansley Review produced by WG33, but benthic organisms face different challenges.

A second objective is to analyse the functional significance of the range of sizes of differentiated cells, including cells which are dead when functioning, which co-exist in multicellular organisms. A question arising from this is whether the organism could benefit functionally from even smaller cells than actually occur, assuming no constraints from the DNA content? A related question is whether polyteny, endopolyploidy and/or multinuclearity is always required in producing the largest differentiated cells in an organism. Among the subjects covered are ploidy changes during the plant/algal life cycle, and the genome size of symbiotic (mycorrhizal) fungi

An important component of the analyses would be to suggest tests of the implications of the phenomena for fitness.

Last Updated April 2009