Understanding the basis of a novel fruit type in Brassicaceae: conservation and deviation in expression patterns of six genes

We identified homologs of ALCATRAZ, FRUITFULL, INDEHISCENT, SHATTERPROOF, and REPLUMLESS from two taxa, representing different types of heteroarthrocarpy. Comparative gene expression of twelve loci was assessed to address how their expression may have been modified to produce heteroarthrocarpy.Studies demonstrated overall conservation in gene expression patterns between dehiscent segments of Erucaria erucarioides and Arabidopsis, with some difference in expression of genes that position the valve margin. In contrast, indehiscence in heteroarthrocarpic fruit segments was correlated with the elimination of the entire valve margin pathway in Erucaria and Cakile lanceolata as well as its absence from a novel lateral abscission zone.These findings suggest that modifications in the valve margin positioning genes are responsible for differences between heteroarthrocarpic and Arabidopsis-like fruits and support the hypothesis that heteroarthrocarpy evolved via repositioning the valve margin. They also highlight conservation in the dehiscence pathway across Brassicaceae.In evolutionary developmental genetic studies, flowers have largely overshadowed fruits despite the fact that fruits display the same diversity in form (reviewed in [1]). Variation in fruit morphology is fundamentally tied to plant dispersal, a key component of angiosperm fitness. Not only have fleshy, dry dehiscent, and dry indehiscent fruits evolved multiple times across flowering plants [2,3], differences in fruit morphology are also observed at close phylogenetic distances within families. For example, berries have evolved more than once in both Solanaceae [4] and Melastomataceae [5]. Even families that have unique fruit types such as Fabaceae (legume) or Brassicaceae (silique) display considerable variation in form, segmentation, shape, and dehiscence capabilities [6-9]. Here we investigate the basis of fruit diversity within the Brassicaceae, the family that houses the genetic model Arabidopsis thaliana