Plastome Organization and Sequence for the Mimosoid Legume Leucaena trichandra

In association with ongoing work on the evolutionary history of Leucaena, we have sequenced the plastome of L. trichandra, one of the first plastome sequences from the diverse Mimosoideae and a species involved in the origin of four tetraploid species of Leucaena. De novo assembly of a 300bp insert paired-end Illumina HiSeq library generated a 164,692bp plastome containing 112 unique genes arranged in the typical large single copy (LSC), inverted repeat, and small single copy regions. The L. trichandra plastome is similar to other legume plastomes in lacking functional rpl22 and rps19 genes, but its LSC is considerably larger.  Previously published legume plastomes all represent Papilionoideae, a group known to harbor various plastome rearrangements.  However, based on this member of the diverse Mimosoideae, there are no large- or small-scale genomic rearrangements when compared to other non-legume rosids or more basal angiosperms. Comparative analyses of mononucleotide, tandem, and dispersed repeats frequencies identified a considerable increase in tandem repeats in L. trichandra, which account for the increased size of the LSC. In contrast, the highly rearranged plastomes of Pelargonium and Trifolium contain a higher number of dispersed repeats.  Rates of mutation among L. trichandra protein coding genes are consistent with most angiosperms plastomes.  The availability of L. trichandra plastome better informs our understanding of legume plastome evolution and it may prove useful to plant breeders interested in using transgenic plastomes and transgene containment strategies in cultivar development.