Complete chloroplast genome sequence of cultivated Morus L. species

Abstract

The complete chloroplast genome (cpDNA) sequences of two cultivated species of Morus L. (Morus atropurpurea and Morus multicaulis) are reported and reconstructed in this study, and were compared with that of wild Morus mongolica. In M. atropurpurea, the circular genome is 159,113 bp in size and comprises two identical inverted repeat (IR) regions of 25,707 bp each, separated by a large single-copy (LSC) region of 87,824 bp and a small single-copy (SSC) region of 19,875 bp. The cpDNA sequence of M. multicaulis is longer than that of M. atropurpurea (159,154 bp), and consists of two IRs (25,678 bp), a LSC region (87,763 bp), and a SSC region (20,035 bp). Each cpDNA contains 112 unique genes including 78 protein-coding genes, 30 transfer RNA genes, and 4 ribosomal RNA genes, with a GC content of 36.2%. There were 83 simple sequence repeats (SSRs) with mononucleotides being the most common (60) and di-, tri-, tetra-, and hexanucleotides appearing less frequently in M. atropurpurea. M. multicaulis contains 81 SSRs containing 63 mononucleotide repeats. The genes and SSRs identified in this study may enhance understanding of cpDNA evolution at both intra- and interspecific levels. MEGA 6.0 was used to construct a phylogenetic tree of 27 species, which revealed that M. atropurpurea and M. multicaulis are more related to their congeners than to others. The cpDNA of M. atropurpurea and M. multicaulis and its structural analysis are important for the chloroplast genome project, development of molecular markers for Morus species, and breeding of varieties.