The Clausena lansium genome provides new insights into alkaloid diversity and the evolution of the methyltransferase family

Wampee(Clausena lansium)is an important evergreen fruit tree native to southern China that has a long history of use for medicinal purposes.Here,a chromosome-level genome of C.lansium was constructed with a genome size of 282.9 Mb and scaffold N50 of 30.75 Mb.The assembled genome contains 48.70%repetitive elements and 24,381 protein-coding genes.Comparative genomic analysis showed that C.lansium diverged from Aurantioideae 15.91-24.95 million years ago.Additionally,some expansive and specific gene families related to methyltransferase activity and S-adenosylmethionine-dependent methyltransferase activity were also identified.Further analysis indicated that N-methyltransferase(NMT)is mainly involved in alkaloid biosynthesis and O-methyltransferase(OMT)participates in the regulation of coumarin accumulation in wampee.This suggested that wampee's richness in alkaloids and coumarins might be due to the gene expansions of NMT and OMT.The tandem repeat event was one of the major reasons for the NMT expansion.Hence,the reference genome of C.lansium will facilitate the identification of some useful medicinal compounds from wampee resources and reveal their biosynthetic pathways.

Aberrant seed development in Litchi chinensis is associated with the impaired expression of cell wall invertase genes

Cell wall invertase(CWIN)are known to play important roles in seed development.However,most reports to date have focused on a single gene family member,and have mainly investigated CWIN functions during the filling stage of seed development.In this study,we found significant lower levels of CWIN protein and activity associated with seed abortion in the Litchi chinensis cultivar“Nuomici.”We identified five litchi CWIN genes and observed that the expression of LcCWIN5 was limited to the flower tissues and decreased sharply with fruit development.Silencing of LcCWIN5 expression before 28 DAA(cell division stage)resulted in perturbed liquid endosperm development,smaller seeds,and higher seed abortion rate,while silencing after 28 DAA(filling stage)had no effect on seed development.In contrast,LcCWIN2 was mostly expressed in the funicle and seed coat,and increased with fruit development.Decreased LcCWIN2 expression and CWIN activity during early seed filling coincided with smaller seeds in the cultivar“Feizixiao.”Silencing of LcCWIN2 caused a reduction in the seed size without inducing seed abortion.We propose that CWIN activity in seed maternal tissues during cell division stage is likely due to LcCWIN5 expression,which regulates early seed development.On the other hand,CWIN activity during the filling stage is due to the expression of LcCWIN2,which may promote carbon import by creating a sucrose gradient.Comparable LcCWIN5 expression,but much lower CWIN activity,detected in the funicle of“Nuomici”is consistent with post-translational regulation.