Genomic insight into domestication of rubber tree.

Understanding the genetic basis of rubber tree (Hevea brasiliensis) domestication is crucial for further improving natural rubber production to meet its increasing demand worldwide. Here we provide a high-quality H. brasiliensis genome assembly (1.58 Gb, contig N50 of 11.21 megabases), present a map of genome variations by resequencing 335 accessions and reveal domestication-related molecular signals and a major domestication trait, the higher number of laticifer rings. We further show that HbPSK5, encoding the small-peptide hormone phytosulfokine (PSK), is a key domestication gene and closely correlated with the major domestication trait. The transcriptional activation of HbPSK5 by myelocytomatosis (MYC) members links PSK signaling to jasmonates in regulating the laticifer differentiation in rubber tree. Heterologous overexpression of HbPSK5 in Russian dandelion (Taraxacum kok-saghyz) can increase rubber content by promoting laticifer formation. Our results provide an insight into target genes for improving rubber tree and accelerating the domestication of other rubber-producing plants.

Extensive sequence divergence between the reference genomes of Taraxacum kok-saghyz and Taraxacum mongolicum.

Plants belonging to the genus Taraxacum are widespread all over the world, which contain rubber-producing and non-rubber-producing species. However, the genomic basis underlying natural rubber (NR) biosynthesis still needs more investigation. Here, we presented high-quality genome assemblies of rubber-producing T. kok-saghyz TK1151 and non-rubber-producing T. mongolicum TM5. Comparative analyses uncovered a large number of genetic variations, including inversions, translocations, presence/absence variations, as well as considerable protein divergences between the two species. Two gene duplication events were found in these two Taraxacum species, including one common ancestral whole-genome triplication and one subsequent round of gene amplification. In genomes of both TK1151 and TM5, we identified the genes encoding for each step in the NR biosynthesis pathway and found that the SRPP and CPT gene families have experienced a more obvious expansion in TK1151 compared to TM5. This study will have large-ranging implications for the mechanism of NR biosynthesis and genetic improvement of NR-producing crops.