Chromosome-level genome assembly of Albizia odoratissima and effect of flavonoid metabolic pathways under drought stress.

Albizia odoratissima is a valuable drought-tolerant native tree species in the dry and hot river valleys of China, which has important ecological and economic values. Exploring its genetic background and phylogenetic direction will be conducive to its further exploitation and use, and promote the process of vegetation restoration in the dry hot river valley region. A genome assembly of approximately 719.88 Mb was achieved at the contig level, featuring a contig N50 of 53.74 Mb. Of this, 98.58% of gene sequences were organized into 13 pseudochromosomes. The A. odoratissima genome contained 96.96% of conserved genes, including 1,538 intact single-copy genes and 42 intact duplicated genes. It had an angiosperm palaeotripling event and the last whole genome duplication event occurred approximately 62.9 million years ago. A. odoratissima shares 8,936 gene families with five other legume species, while 1,420 gene families are unique to A. odoratissima. Under drought stress, photosynthesis was significantly inhibited to reduce water consumption, osmoregulatory substances were significantly increased to alleviate osmotic stress, and flavonoid accumulation was induced to enhance antioxidant capacity through the up-regulation of AoANS (Aod07G019900) gene expression, thereby improving drought tolerance. High-quality reference genomes generated through molecular studies are advancing research into the molecular mechanisms of A. odoratissima.