Comparative analysis of Miscanthus and Saccharum reveals a shared whole-genome duplication but different evolutionary fates

Abstract

Multiple polyploidizations with divergent consequences in the grass subtribe Saccharinae provide a singular opportunity to study in situ adaptation of a genome to the duplicated state, heretofore known primarily from paleogenomics. We show that allopolyploidy in a common Miscanthus-Saccharumancestor ~3.8 to 4.6 million years ago closely coincides in time with their divergence from the Sorghumlineage. Subsequent Saccharum-specific autopolyploidy may have created pseudo-paralogous chromosome groups with random pairing within a group but infrequent pairing between groups. High chromosome number may reduce differentiation among Saccharumpseudo-paralogs by increasing opportunities for recombinations, with the lower chromosome numbers of Miscanthusfavoring the return to disomic inheritance. The widespread tendency of plant chromosome numbers to recursively return to a narrow range following genome duplication appears to be occurring now in Saccharum spontaneum based on rich polymorphism for chromosome number among genotypes, with past reductions indicated by condensations of two ancestral chromosomes in Miscanthus (now n= 19) and perhaps as many as 10 in the Narenga-Sclerostachyaclade (n= 15). © 2014 American Society of Plant Biologists. All rights reserved.