Organ-wise homologies of stipule, leaf and inflorescence between Pisum sativum genetic variants, Delonix regia and Caesalpinia bonduc indicate parallel evolution of morphogenetic regulation

Abstract

Plants of the garden pea Pisum sativum an annual Papilionaceae species which have a mutation in the COCHLEATA (COCH) gene bear compound stipules of leaf morphology and secondary inflorescences in which flowers are borne in axils of bracteoles on an inflorescence stem. In the wild-type P. sativum stipules are simple foliaceous and flowers are non-bracteolated. Mutants of the coch phenotype are not known in any other plant species. The COCH gene of P. sativum is not yet sequenced. Therefore whether or not the COCH gene is present in species other than P. sativum remains unknown. Based on the principle of parallel evolution, it is thought that there may be leguminous species that possess the coch phenotype. In search of coch species, the Leguminosae flora of Delhi was surveyed for species that demonstrate compound stipules and bracteolated inflorescences. Out of 124 reported in the Leguminosae flora of Delhi, only the perennial Caesalpinioideae tree species Delonix regia and the shrubby vine species Caesalpinia bonduc were observed to have features of the coch mutants of P. sativum. Since the traits of simple foliaceous stipules and bracteoleless secondary inflorescences of wild-type P. sativum are common to many species among more than 19,400 species of family Leguminosae, it is hypothesized that the COCH gene may be as common as the ubiquitously present LEAFY gene (orthologue of UNIFOLIATA gene of P. sativum) in angiosperms.