The Multipartite Mitochondrial Genome of Marama (Tylosema esculentum)

Tylosema esculentum (marama bean), a wild legume from tropical Africa, has long been considered as a potential crop for local farmers due to its rich nutritional value. Genomics research of marama is indispensable for the domestication and varietal improvement of the bean. The chloroplast genome of marama has been sequenced and assembled previously using a hybrid approach based on both Illumina and PacBio data. In this study, a similar method was used to assemble the mitochondrial genome of marama. The mitochondrial genome of the experimental individual has been confirmed to have two large circles OK638188 and OK638189, which do not recombine according to the data. However, they may be able to restructure into five smaller circles through recombination on the 4 pairs of long repeats (>1 kb). The total length of marama mitogenome is 399,572 bp. A 9,798 bp DNA fragment has been found that is homologous to the chloroplast genome of marama, accounting for 2.5% of the mitogenome. In the Fabaceae family, the mitogenome of Millettia pinnata is highly similar to marama, including for both the genes present and the total size. Some genes including cox2, rpl10, rps1, and sdh4 have been lost during the evolution of angiosperms and are absent in the mitogenomes of some legumes. However, these remain intact and functional in marama. Another set of genes, rpl2, rps2, rps7, rps11, rps13, and rps19 are either absent, or present as pseudogenes, in the mitogenome of marama.

Lotus japonicus symbiosis signaling genes and their role in the establishment of root-associated bacterial and fungal communities

The wild legume Lotus japonicus engages in mutualistic symbiotic relationships with arbuscular mycorrhiza (AM) fungi and nitrogen-fixing rhizobia. Using plants grown in natural soil and community profiling of bacterial 16S rRNA genes and fungal internal transcribed spacers (ITS), we examined here the role of the Lotus symbiosis genes RAM1, NFR5, SYMRK, and CCaMK in structuring bacterial and fungal root-associated communities. We found host genotype-dependent community shifts in the root and rhizosphere compartments that were mainly confined to bacteria in nfr5 or fungi in ram1 mutants, whilst symRK and ccamk plants displayed major changes across both microbial kingdoms. We observed in all AM mutant roots an almost complete depletion of a large number of Glomeromycota taxa that was accompanied by a concomitant enrichment of Helotiales and Nectriaceae fungi, suggesting compensatory niche replacement within the fungal community. A subset of Glomeromycota whose colonization is strictly dependent on the common symbiosis pathway was retained in ram1 mutants, indicating that RAM1 is dispensable for intraradical colonization by some Glomeromycoyta fungi. However, intraradical colonization by certain Burkholderiaceae taxa is dependent on AM root infection, thereby revealing a microbial interkingdom interaction. Our findings imply a broad role for Lotus symbiosis genes in structuring the root microbiota.