Screening for leaf‐associated endophytes in the genus P sychotria ( R ubiaceae )

B urkholderia endophytes were identified within the leaves of non‐nodulated members of the genus P sychotria . In contrast to leaf‐nodulated P sychotria species, which are known to accommodate their endosymbionts into specialized endosymbiont‐housing structures, non‐nodulated species lack bacterial leaf nodules and harbor endosymbionts intercellularly between mesophyll cells. Based on molecular data ( rps16 , trnG , and trnLF ), the phylogenetic reconstruction of the host plants revealed a separate origin of leaf‐nodulated and non‐nodulated P sychotria species. Despite a distinct phylogenetic position of the two host clades, the endophytes of the non‐nodulated plants were not placed into a single monophyletic group but were found to be closely related to the leaf‐nodulated endosymbionts. The observation of genetically similar endophytes in both nodulated and non‐nodulated P sychotria lineages suggests that the host plant is playing a crucial role in the induction of leaf nodule formation. Moreover, the concentration of endosymbionts into specialized leaf nodules may be considered as a more derived evolutionary adaptation of the host plant, serving as an interface structure to facilitate metabolic exchange between plant and endosymbiont.