Yang, Z.-L. | Search bioRxiv

bioRxiv2021

Evolutionary innovations through gain and loss of genes in the ectomycorrhizal Boletales

O_LIIn this study, we aim to identify genomic traits of the transitions to the ectomycorrhizal ecology within the Boletales, one of the most diverse lineages of symbiotrophic fungi. C_LIO_LIWe sequenced the genomes and compared the gene repertoires of symbiotrophic Boletales species to their saprotrophic brown-rot relatives. We also reconstructed gene duplication/loss histories along a time-calibrated phylogeny. C_LIO_LIWe showed that the rate of gene duplication is constant along the backbone of Boletales phylogeny with large loss events in lineages leading to several families. The rate of gene family expansion sharply increased in the late Miocene and mostly took place in Boletaceae. C_LIO_LIMost of the ectomycorrhizal Boletales are characterized by a large genome size due to transposable element (TE) expansions and a reduction in the diversity of plant cell wall degrading enzymes (PCWDEs) compared to their brown-rot relatives. However, several species in the Boletaceae, Paxillaceae and Boletinellaceae have kept a substantial set of endoglucanases and LPMOs acting on cellulose/hemicellulose and fungal polysaccharides suggesting that they may partly decompose organic matter by a combined activity of oxidative and hydrolytic enzymes. C_LIO_LIThe present study provides novel insights on our understanding of the mechanisms that influence the evolutionary diversification of boletes and symbiosis evolution. C_LI

genomics↗

bioRxiv2021

Sugar transporters enable a leaf beetle to accumulate plant defense compounds

Many herbivorous insects selectively accumulate plant toxins for defense against predators; however, little is known about the transport processes that enable insects to absorb and store defense compounds in the body. Here, we investigate how a specialist herbivore, the horseradish flea beetle, accumulates high amounts of glucosinolate defense compounds in the hemolymph. Using phylogenetic analyses of coleopteran membrane transporters of the major facilitator superfamily, we identified a clade of glucosinolate-specific transporters (PaGTRs) belonging to the sugar porter family. PaGTR expression was predominantly detected in the excretory system, the Malpighian tubules. Silencing of PaGTRs led to elevated glucosinolate excretion, significantly reducing the levels of sequestered glucosinolates in beetles. This suggests that PaGTRs reabsorb glucosinolates from the Malpighian tubule lumen to prevent their loss by excretion. Ramsay assays performed with dissected Malpighian tubules confirmed a selective retention of glucosinolates. Thus, the selective accumulation of plant defense compounds in herbivorous insects can depend on the ability to prevent excretion.

physiology↗