Evidence that an evolutionary transition from dehiscent to indehiscent fruits in L epidium ( B rassicaceae) was caused by a change in the control of valve margin identity genes

Summary In the B rassicaceae, indehiscent fruits evolved from dehiscent fruits several times independently. Here we use closely related wild species of the genus L epidium as a model system to analyse the underlying developmental genetic mechanisms in a candidate gene approach. ALCATRAZ ( ALC ), INDEHISCENT ( IND ), SHATTERPROOF 1 ( SHP 1 ) and SHATTERPROOF 2 ( SHP 2 ) are known fruit developmental genes of A rabidopsis thaliana that are expressed in the fruit valve margin governing dehiscence zone formation. Comparative expression analysis by quantitative RT ‐ PCR , Northern blot and in situ hybridization show that their orthologues from L epidium campestre (dehiscent fruits) are similarly expressed at valve margins. In sharp contrast, expression of the respective orthologues is abolished in the corresponding tissue of indehiscent L epidium appelianum fruits, indicating that changes in the genetic pathway identified in A . thaliana caused the transition from dehiscent to indehiscent fruits in the investigated species. As parallel mutations in different genes are quite unlikely, we conclude that the changes in gene expression patterns are probably caused by changes in upstream regulators of ALC , IND and SHP 1 / 2 , possible candidates from A . thaliana being FRUITFULL ( FUL ), REPLUMLESS ( RPL ) and APETALA 2 ( AP 2 ). However, neither expression analyses nor functional tests in transgenic plants provided any evidence that the FUL or RPL orthologues of L epidium were involved in evolution of fruit indehiscence in L epidium . In contrast, stronger expression of AP 2 in indehiscent compared to dehiscent fruits identifies AP 2 as a candidate gene that deserves further investigation.