AUTHOR=Manatunga Sachini Lakmini , Furtado Agnelo , Topp Bruce , Alam Mobashwer , Mason Patrick J. , Kharabian-Masouleh Ardashir , Henry Robert J. 

TITLE=Analysis of phylogenetic relationships in Macadamia shows evidence of extensive reticulate evolution

JOURNAL=Frontiers in Plant Science

VOLUME=15

YEAR=2024

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2024.1394244

DOI=10.3389/fpls.2024.1394244

ISSN=1664-462X

ABSTRACT=<p>The genus <italic>Macadamia</italic> in the Proteaceae family includes four species native to Australia. Two of the four species, <italic>M. integrifolia</italic> and <italic>M. tetraphylla</italic>, have recently been utilized to generate domesticated macadamia varieties, grown for their edible nuts. To explore diversity in macadamia genetic resources, a total of 166 wild genotypes, representing all four species, were sequenced. The four species were clearly distinguished as four separate clades in a phylogenetic analysis of the nuclear genome (based upon concatenated nuclear gene CDS and SNPs). The two larger species (<italic>M. integrifolia</italic> and <italic>M. tetraphylla</italic>) formed a clade, that had diverged from a clade including the smaller species (<italic>M. ternifolia</italic> and <italic>M. jansenii</italic>). The greatest diversity in nuclear and chloroplast genomes was found in the more widely distributed <italic>M. integrifolia</italic> while the rare <italic>M. jansenii</italic> showed little diversity. The chloroplast phylogeny revealed a much more complex evolutionary history. Multiple chloroplast capture events have resulted in chloroplast genome clades, including genotypes from different species. This suggests extensive reticulate evolution in <italic>Macadamia</italic> despite the emergence of the four distinct species that are supported by the analysis of their nuclear genomes. The chloroplast genomes showed strong associations with geographical distribution reflecting limited maternal gene movement in these species that have large seeds. The nuclear genomes showed lesser geographical differences, probably reflecting the longer distance pollen movement. This improved understanding of the distribution of diversity in <italic>Macadamia</italic> will aid in the conservation of these rare species now found in highly fragmented rainforest remnants.</p>