Phylogeny of Maleae (Rosaceae) Based on Complete Chloroplast Genomes Supports the Distinction of Aria, Chamaemespilus and Torminalis as Separate Genera, Different from Sorbus sp

Refining the phylogeny and taxonomy of the apple tribe Maleae (Rosaceae): insights from phylogenomic analyses of 563 plastomes and a taxonomic synopsis of Photinia and its allies in the Old World

This study addresses the longstanding absence of a comprehensive phylogenetic backbone for the apple tribe Maleae, a deficiency attributed to limited taxon and marker sampling. We conducted an extensive taxon sampling, incorporating 563 plastomes from a diverse range of 370 species encompassing 26 presently recognized genera. Employing a range of phylogenetic inference methods, including RAxML and IQ-TREE2 for Maximum Likelihood (ML) analyses, we established a robust phylogenetic framework for the Maleae tribe. Our phylogenomic investigations provided compelling support for three major clades within Maleae. By integrating nuclear phylogenetic data with morphological and chromosomal evidence, we propose an updated infra-tribal taxonomic system, comprising subtribe Malinae Reveal, subtribe Lindleyinae Reveal, and subtribe Vauqueliniinae B.B.Liu (subtr. nov.). Plastid phylogenetic analysis also confirmed the monophyly of most genera, except for Amelanchier, Malus, Sorbus sensu lato, and Stranvaesia. In addition, we present a comprehensive taxonomic synopsis of Photinia and its morphological allies in the Old World, recognizing 27 species and ten varieties within Photinia, three species and two varieties within Stranvaesia, and two species and three varieties within Weniomeles. Furthermore, we also lectotypified 12 names and made two new combinations, Photiniamicrophylla (J.E.Vidal) B.B.Liu and Weniomelesatropurpurea (P.L.Chiu ex Z.H.Chen & X.F.Jin) B.B.Liu.

Biphenyls and dibenzofurans of the rosaceous subtribe Malinae and their role as phytoalexins

MAIN CONCLUSION

Biphenyl and dibenzofuran phytoalexins are differentially distributed among species of the rosaceous subtribe Malinae, which includes apple and pear, and exhibit varying inhibitory activity against phytopathogenic microorganisms. Biphenyls and dibenzofurans are specialized metabolites, which are formed in species of the rosaceous subtribe Malinae upon elicitation by biotic and abiotic inducers. The subtribe Malinae (previously Pyrinae) comprises approximately 1000 species, which include economically important fruit trees such as apple and pear. The present review summarizes the current status of knowledge of biphenyls and dibenzofurans in the Malinae, mainly focusing on their role as phytoalexins. To date, 46 biphenyls and 41 dibenzofurans have been detected in 44 Malinae species. Structurally, 54 simple molecules, 23 glycosidic compounds and 10 miscellaneous structures were identified. Functionally, 21 biphenyls and 21 dibenzofurans were demonstrated to be phytoalexins. Furthermore, their distribution in species of the Malinae, inhibitory activities against phytopathogens, and structure-activity relationships were studied. The most widely distributed phytoalexins of the Malinae are the three biphenyls aucuparin (3), 2'-methoxyaucuparin (7), and 4'-methoxyaucuparin (9) and the three dibenzofurans α-cotonefuran (47), γ-cotonefuran (49), and eriobofuran (53). The formation of biphenyl and dibenzofuran phytoalexins appears to be an essential defense weapon of the Malinae against various stresses. Manipulating phytoalexin formation may enhance the disease resistance in economically important fruit trees. However, this approach requires an extensive understanding of how the compounds are formed. Although the biosynthesis of biphenyls was partially elucidated, formation of dibenzofurans remains largely unclear. Thus, further efforts have to be made to gain deeper insight into the distribution, function, and metabolism of biphenyls and dibenzofurans in the Malinae.

Complete chloroplast genomes of Sorbus sensu stricto (Rosaceae): comparative analyses and phylogenetic relationships

BACKGROUND

Sorbus sensu stricto (Sorbus s.s.) is a genus with important economical values because of its beautiful leaves, and flowers and especially the colorful fruits. It belongs to the tribe Maleae of the family Rosaceae, and comprises about 90 species mainly distributed in China. There is on-going dispute about its infrageneric classification and species delimitation as the species are morphologically similar. With the aim of shedding light on the circumscription of taxa within the genus, phylogenetic analyses were performed using 29 Sorbus s.s. chloroplast (cp) genomes (16 newly sequenced) representing two subgenera and eight sections.

RESULTS

The 16 cp genomes newly sequenced range between 159,646 bp and 160,178 bp in length. All the samples examined and 22 taxa re-annotated in Sorbus sensu lato (Sorbus s.l.) contain 113 unique genes with 19 of these duplicated in the inverted repeat (IR). Six hypervariable regions including trnR-atpA, petN-psbM, rpl32-trnL, trnH-psbA, trnT-trnL and ndhC-trnV were screened and 44-53 SSRs and 14-31 dispersed repeats were identified as potential molecular markers. Phylogenetic analyses under ML/BI indicated that Sorbus s.l. is polyphyletic, but Sorbus s.s. and the other five segregate genera, Aria, Chamaemespilus, Cormus, Micromeles and Torminalis are monophyletic. Two major clades and four sub-clades resolved with full-support within Sorbus s.s. are not consistent with the existing infrageneric classification. Two subgenera, subg. Sorbus and subg. Albocarmesinae are supported as monophyletic when S. tianschanica is transferred to subg. Albocarmesinae from subg. Sorbus and S. hupehensis var. paucijuga transferred to subg. Sorbus from subg. Albocarmesinae, respectively. The current classification at sectional level is not supported by analysis of cp genome phylogeny.

CONCLUSION

Phylogenomic analyses of the cp genomes are useful for inferring phylogenetic relationships in Sorbus s.s. Though genome structure is highly conserved in the genus, hypervariable regions and repeat sequences used are the most promising molecule makers for population genetics, species delimitation and phylogenetic studies.

Taxonomic notes on Sorbusmegalocarpa (Rosaceae) and related taxa

Four Sorbus taxa endemic to China, S.arguta, S.guanxianensis, S.megalocarpavar.megalocarpa and S.megalocarpavar.cuneata, are morphologically similar to one another in having large brown fruits with persistent calyx and dense lenticels. In literature, either all of the four taxa were accepted, or two of them, S.arguta and S.megalocarpavar.cuneata, were treated as synonyms of S.megalocarpavar.megalocarpa, or S.guanxianensis alone was dubious. In this study, based on morphological comparison, S.arguta is reinstated for its relatively small inflorescence, small fruit and timing of flowering after leaves are unfolded. S.megalocarpavar.cuneata is confirmed as a synonym and S.guanxianensis is proposed as a new heterotypic synonym of S.megalocarpa.