Extending functional understanding from Arabidopsis to Brassica genomes:
As the first plant genome to be sequenced, the Arabidopsis thaliana genome is a reference for plant comparative genomics. An emerging question in agriculture is the degree to which breeding will be informed by results from the model plant Arabidopsis. A logical starting point for this endeavor is in the Brassica oilseed crops. Comparisons of the two genomes show large regions of synteny, where segments of Arabidopsis chromosomes are present, often in triplicate, in the diploid Brassica species genomes. Recent work comparing genomes across the family Brassicaceae reconstructs eight ancestral chromosomes that rearranged into the current chromosome numbers found in the family. This evolutionary perspective shows that much of the difference between the Arabidopsis and Brassica genomes is due to rearrangements in the Arabidopsis lineage that occurred after the split from Brassica approximately 20 million years ago.
We are working to identify genomic regions in the Brassica species that are homologous to all twelve already identified drought avoidance QTL in Arabidopsis. We are focusing on the easiest approach, finding homologous regions in the diploid species Brassica rapa, which is currently being sequenced. The B. rapa genome is found not only in B. rapa, but also in the allotetraploid species Brassica napus (a major oilseed crop). To date, syntenic regions or blocks of the Arabidopsis genome have been identified for over 90% of the B. napus linkage map. The screening for homologous regions will be done using eight varieties of B. rapa, as well as spring and winter varieties of B. napus. Homozygous lines will be germinated in the greenhouse and transplanted into a field experiment at the CSU-USDA site in Akron, OH. Later, these plants will also be grown in controlled environment chambers. Effects of QTL on yield and physiological genotypes such as carbon isotope ratio will be determined using simple statistical contrasts between the two homozygous classes within a given cross.
