8) Plant evo devo (by Theodor Zbinden)

The most work made on Evolutionary Developmental (evo devo) Biology until recently was made on the known model organisms like Drosophila melanogaster, C. elegans, zebrafish and Xenopus laevis.  However in the last couple of years much information about evo devo was also made on plants to better understand plant morphology and development patterns.

The ABC model is a system of floral development, established in the 1980.  The model describes how the structure of a flower emerges and which genes are involved in this formation.  A normal flower normally consists of sepals, petals, stamens and carpels.  For each of these organs exists specific genes grouped in A, B or C class.  Induced genetic mutations helped establish this model in which different genes were assigned to A, B or C classes, depending on their phenotypic change produced after mutating a particular gene.  In this older model the A gens are involved in the production of the sepal, the A and B genes for petals, the B and C genes for Stamens and the C gens for the production of the carpels. 

Fig. A: The ABC model system of floral development

However, this model was revised and now there are two more, D and E classes of genes, involved in the development of the flower.  Today A and E genes are needed for sepal production, the A, B and E genes for petal production.  For the production of stamens the B, C and E genes are responsible and the C and E genes are required for carpel.  And finally the C, D and E are responsible for the ovules inside the carpels.  Nevertheless, as everything in science this may change over time as new genes will be discovered in other non-model species.

  Fig. B: The ABCDE model system of floral development

An example of evo devo in plants is the investigation project that studies genes responsible for the carpel development.  The carpel is the reproductive structure of the female plant that encloses the eggs and that develops after in seedpods and fruits.  The problem is that the evolutionary origin of the carpel is not clear.  To better understand this origin they study on more primitive plants like Eschscholzia californica (California poppy).  This plant has the advents that it can be manipulated transgenically.  The goal is to identify and characterize genes responsible for carpel development.  Comparison between Eschscholzia californica and the model organism Arabidopsis can help reveal genes underlying in carpel development of flowering plants.

The flower of the plants is one of the amazing innovations of nature to diversify the angiosperms.  Because of their importance of flowering plants as a food source for humans it is important to understand there evolution and development.  The floral structure is mainly constructed of four organ types, sepals, petals, stamens and carpel.  The interesting fact is that these four structures can acquire a wide variety of forms and changes.  Some of these changes can be the abortion of the organ, radial versus bilateral symmetry, dramatic changes in the color patterns, changes in the number and size of the floral organs or it can even develop new floral organs.  Because of these interesting changes in the flowering organs it is an interesting field for evo devo researchers to study such interesting phenomenon.  The results gained on such plant organ changes will contribute significantly on the understanding of morphology, developmental comparative studies and phylogenetic analyses on model and non-model plants.

                                                         Plant Evolutionary Developmental (10 min)          

                                                            (Plant Evolution (21min)

References:

        J. L. Bowman, D. R. Smyth and E. M. Meyerowitz (2012). The ABC model of flower development: then and now.         

                    Development 139, 4095-4098
              The ABC model (2009), Building Beauty vol. 175, #8. D. E. Soltis ed al. (2007), The ABC Model and its Applicability to            

                    Basal Angiosperms. Ann Bot 100 (2): 155-163.