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Research Reveals the Origin- Dispersal Areas of Toddalia Species

2022-03-29

Toddalia is a monotypic genus consisting of sole species Toddalia asiatica (L.) Lam., widely distributed in Africa and Asia. It belongs to the family Rutaceae. This genus together with genera Phellodendron Rupr., Tetradium Lour., and Zanthoxylum L. were found to produce alkaloids. The four genera have attracted the attention of many scientists and they have been studied widely in previous studies. However, there is insufficient genomic resources in this genus. Additionally the origin and dispersal points of Toddalia species remains unclear.

Supervised by Prof. HU Guangwan from Wuhan Botanical Garden, student MUTINDA Elizabeth Syowai from Kenyan carried out the study of comparative genomics, phylogenetics, and biogeography of two samples of T. asiatica collected from Kenya and T. asiatica from Asia available in the NCBI (National Center of Biotechnology Information) database.

This research finds that the complete chloroplast (cp) genome of T. asiatica from Africa has 158, 508 base pairs, with a large single-copy region, small single-copy region and two inverted repeat regions. The genome contains 113 genes. Comparative analysis displays high similarity in gene arrangement of both species from Africa and Asia. The three most divergent hotspot regions observed are trnH-psbA, rpoB, and ycf1 genes, which demonstrate their ability as potential barcode makers for phylogenetic analysis studies and plant identification. Both Toddalia species are represented with strongly supported phylogenetic trees using maximum likelihood (ML) and Bayesian inference (BI) analysis. The results support the merging of the genus Toddalia with Zanthoxylum and taxonomic change of Toddalia asiatica to Zanthoxylum asiaticum.

Moreover, biogeographic analysis indicates an Asian origin of Toddalia species and later dispersal to Africa and Madagascar. The maxent models shows that Asia would have a favorable climate for Toddalia species in the future. In Africa, there will be contraction and expansion of the favorable areas for these species.

This work provides insight into the availability of the cp genomes in Rutaceae, which could be helpful for further population genetics and biogeographic studies of these species.

The research entitled “Comparative Genomics, Phylogenetics, Biogeography, and Effects of Climate Change on Toddalia asiatica (L.) Lam. (Rutaceae) from Africa and Asia” was published in plants. This work was supported by the International Partnership Program of the Chinese Academy of Sciences (CAS), the National Natural Science Foundation of China and Sino-Africa Joint Research Center, CAS.

Kenyan student Elizabeth Syowai Mutinda is the first author. Professor HU Guangwan is the corresponding author. Several students from the group participated in the study.

Gene map of Toddalia plastomes (Image by WBG)

A sliding window analysis of nucleotide variability (Pi) values of different regions of Toddalia (Image by WBG)

Comparison of the borders of large single copy (LSC), small single copy, (SSC), and inverted repeat (IR) regions among the Toddalia plastomes (Image by WBG)

Phylogenetic tree construction of 35 taxa using maximum likelihood (ML) and Bayesian inference (BI) methods using 79 protein-coding genes (Image by WBG)

Maps showing distribution modeling for Toddalia asiatica for the years 2050 and 2070 (Image by WBG)