Morphological diversity and genetic regulation of inflorescence abscission zones in grasses

Premise of the study: Variation in how seeds are dispersed in grasses is ecologically important, and selection for dispersal mechanisms has produced a great variety of dispersal structures (diaspores). Abscission (“shattering”) is necessary in wild grasses, but its elimination by selection on nonshattering mutants was a key component of the domestication syndrome in cereal grasses. A key question is whether a common genetic pathway controls abscission in wild grasses, and, if so, what genes in that pathway may have been selected upon during domestication. We summarize morphological and genetic information on abscission zones and disarticulation patterns in grasses and identify hypotheses to test the likelihood of a common genetic pathway.

Methods: Morphological data on abscission zones for over 10 000 species of grasses were tabulated and analyzed using a tribal phylogeny of the grasses. The genomic location of quantitative trait loci (QTLs) and orthologs of genes controlling shattering were compared across species to ascertain whether the same loci might control shattering in different grass lineages.

Results and conclusions: The simple trait of nonshattering is derived from a great diversity of shattering phenotypes. Several sets of QTLs from multiple species are syntenic yet many are not. Genes known to be involved in shattering in several species were found to have orthologs that sometimes colocalized with QTLs in different species, adding support to the hypothesis of retention of a common genetic pathway. These results are used to suggest a research plan that could test the common genetic pathway model more thoroughly.