AUTHOR=Zeng Qiwei , Chen Miao , Wang Shouchang , Xu Xiaoxiang , Li Tian , Xiang Zhonghuai , He Ningjia 

TITLE=Comparative and phylogenetic analyses of the chloroplast genome reveal the taxonomy of the Morus genus

JOURNAL=Frontiers in Plant Science

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.1047592

DOI=10.3389/fpls.2022.1047592

ISSN=1664-462X

ABSTRACT=<p>Mulberry (genus <italic>Morus</italic>) is an economically important woody plant with an altered ploidy level. The variable number of <italic>Morus</italic> species recognized by different studies indicates that the genus is in need of revision. In this study, the chloroplast (CP) genomes of 123 <italic>Morus</italic> varieties were <italic>de novo</italic> assembled and systematically analyzed. The 123 varieties represented six <italic>Morus</italic> species, namely, <italic>Morus alba</italic>, <italic>Morus nigra</italic>, <italic>Morus notabilis</italic>, <italic>Morus rubra</italic>, <italic>Morus celtidifolia</italic>, and <italic>Morus serrata</italic>. The <italic>Morus</italic> CP genome was found to be 158,969~159,548 bp in size with 125 genes, including 81 protein coding, 36 tRNA, and 8 rRNA genes. The 87 out of 123 mulberry accessions were assigned to 14 diverse groups with identical CP genome, which indicated that they are maternally inherited and share 14 common ancestors. Then 50 diverse CP genomes occurred in 123 mulberry accessions for further study. The CP genomes of the <italic>Morus</italic> genus with a quadripartite structure have two inverted repeat (IR) regions (25,654~25,702 bp) dividing the circular genome into a large single-copy (LSC) region (87,873~88,243 bp) and small single-copy (SSC) region (19,740~19,994 bp). Analysis of the phylogenetic tree constructed using the complete CP genome sequences of <italic>Morus</italic> revealed a monophyletic genus and that <italic>M. alba</italic> consisted of two clades, <italic>M. alba</italic> var. <italic>alba</italic> and <italic>M. alba</italic> var. <italic>multicaulis</italic>. The Japanese cultivated germplasms were derived from <italic>M. alba</italic> var. <italic>multicaulis</italic>. We propose that the <italic>Morus</italic> genus be classified into six species, <italic>M. nigra</italic>, <italic>M. notabilis</italic>, <italic>M. serrata</italic>, <italic>M. celtidifolia</italic>, <italic>M. rubra</italic>, and <italic>M. alba</italic> with two subspecies, <italic>M. alba</italic> var. <italic>alba</italic> and <italic>M. alba</italic> var. <italic>multicaulis</italic>. Our findings provide a valuable resource for the classification, domestication, and breeding improvement of mulberry.</p>