Chromosome-scale assembly of the Moringa oleifera Lam. genome uncovers polyploid history and evolution of secondary metabolism pathways through tandem duplication

Abstract

The African Orphan Crops Consortium (AOCC) selected the highly nutritious, fast growing and drought tolerant tree crop moringa (Moringa oleifera Lam.) as one of the first of 101 plant species to have its genome sequenced and a first draft assembly was published in 2019. Given the extensive uses and culture of moringa, often referred to as the multipurpose tree, we generated a significantly improved new version of the genome based on long-read sequencing into 14 pseudochromosomes equivalent to n = 14 haploid chromosomes. We leveraged this nearly complete version of the moringa genome to investigate main drivers of gene family and genome evolution that may be at the origin of relevant biological innovations including agronomical favorable traits. Our results reveal that moringa has not undergone any additional whole-genome duplication (WGD) or polyploidy event beyond the gamma WGD shared by all core eudicots. Moringa duplicates retained following that ancient gamma events are also enriched for functions commonly considered as dosage balance sensitive. Furthermore, tandem duplications seem to have played a prominent role in the evolution of specific secondary metabolism pathways including those involved in the biosynthesis of bioactive glucosinolate, flavonoid, and alkaloid compounds as well as of defense response pathways and might, at least partially, explain the outstanding phenotypic plasticity attributed to this species. This study provides a genetic roadmap to guide future breeding programs in moringa, especially those aimed at improving secondary metabolism related traits.