Identification and functional characterization of ApisOr23 in pea aphid Acyrthosiphon pisum

Pea aphid,Acyrthosiphon pisum,is a serious pest of many different leguminous plants,and it mainly relies on its odorant receptors(Ors)to discriminate among host species.However,less is known about the role that Ors play in the host plant location.In this study,we identified a novel conserved odorant receptor clade by phylogenetic analysis,and conducted the functional analysis of ApisOr23 in A.pisum.The results showed that the homologous Ors from A.pisum,Aphis glycines and Aphis gossypii share 94.28% identity in amino acid sequences.Moreover,conserved motifs were analyzed using the annotated homologous Or23 from eight aphid species,providing further proof of the high conservation level of the Or23 clade.According to the tissue expression pattern analysis,ApisOr23 was mainly expressed in the antennae.Further functional study using a heterologous Xenopus expression system revealed that ApisOr23 was tuned to five plant volatiles,namely trans-2-hexen-1-al,cis-2-hexen-1-ol,1-heptanol,4’-ethylacetophenone,and hexyl acetate.Among them,trans-2-hexen-1-al,which is one of the main volatile organic compounds released from legume plants,activated the highest response of ApisOr23.Our findings suggest that the conserved Or23 clade in most aphid species might play an important role in host plant detection.

A conserved odorant receptor identified from antennal transcriptome of Megoura crassicauda that specifically responds to cis-jasmone

Herbivore-induced plant volatiles(HIPVs)play a key role in the interactions between plants and herbivorous insects,as HIPVs can promote or deter herbivorous insects’behavior.While aphids are common and serious phloem-feeding pests in farmland ecosystems,little is known about how aphids use their sensitive olfactory system to detect HIPVs.In this study,the antennal transcriptomes of the aphid species Megoura crassicauda were sequenced,and expression level analyses of M.crassicauda odorant receptors(ORs)were carried out.To investigate the chemoreception mechanisms that M.crassicauda uses to detect HIPVs,we performed in vitro functional studies of the ORs using 11 HIPVs reported to be released by aphid-infested plants.In total,54 candidate chemosensory genes were identified,among which 20 genes were ORs.McraOR20 and McraOR43 were selected for further functional characterization because their homologs in aphids were quite conserved and their expression levels in antennae of M.crassicauda were relatively high.The results showed that McraOR20 specifically detected cis-jasmone,as did its ortholog ApisOR20 from the pea aphid Acyrthosiphon pisum,while McraOR43 did not respond to any of the HIPV chemicals that were tested.This study characterized the ability of the homologous OR20 receptors in the two aphid species to detect HIPV cis-jasmone,and provides a candidate olfactory target for mediating aphid behaviors.

The genomes of seven economic Caesalpinioideae trees provide insights into polyploidization history and secondary metabolite biosynthesis

The Caesalpinioideae subfamily contains many well-known trees that are important for economic sustainability and human health,but a lack of genomic resources has hindered their breeding and utilization.Here,we present chromosome-level reference genomes for the two food and industrial trees Gleditsia sinensis(921 Mb)and Biancaea sappan(872 Mb),the three shade and ornamental trees Albizia julibrissin(705 Mb),Delonix regia(580 Mb),and Acacia confusa(566 Mb),and the two pioneer and hedgerow trees Leucaena leucocephala(1338 Mb)and Mimosa bimucronata(641 Mb).Phylogenetic inference shows that the mimosoid clade has a much higher evolutionary rate than the other clades of Caesalpinioideae.Macrosynteny comparison suggests that the fusion and breakage of an unstable chromosome are responsible for the difference in basic chromosome number(13 or 14)for Caesalpinioideae.After an ancient whole-genome duplication(WGD)shared by all Caesalpinioideae species(CWGD,~72.0 million years ago[MYA]),there were two recent successive WGD events,LWGD-1(16.2-19.5 MYA)and LWGD-2(7.1-9.5 MYA),in L.leucocephala.Thereafter,~40%gene loss and genome-size contraction have occurred during the diploidization process in L.leucocephala.To investigate secondary metabolites,we identified all gene copies involved in mimosine metabolism in these species and found that the abundance of mimosine biosynthesis genes in L.leucocephala largely explains its high mimosine production.We also identified the set of all potential genes involved in triterpenoid saponin biosynthesis in G.sinensis,which is more complete than that based on previous transcriptome-derived unigenes.Our results and genomic resources will facilitate biological studies of Caesalpinioideae and promote the utilization of valuable secondary metabolites.

Haplotype-resolved chromosome-level genome of hexaploid Jerusalem artichoke provides insights into its origin,evolution,and inulin metabolism

Jerusalem artichoke(Helianthus tuberosus)is a global multifunctional crop.It has wide applications in the food,health,feed,and biofuel industries and in ecological protection;it also serves as a germplasm pool for breeding of the global oil crop common sunflower(Helianthus annuus).However,biological studies of Je-rusalem artichoke have been hindered by a lack of genome sequences,and its high polyploidy and large genome size have posed challenges to genome assembly.Here,we report a 21-Gb chromosome-level as-sembly of the hexaploid Jerusalem artichoke genome,which comprises 17 homologous groups,each with 6 pseudochromosomes.We found multiple large-scale chromosome rearrangements between Jerusalem artichoke and common sunflower,and our results show that the hexaploid genome of Jerusalem artichoke was formed by a hybridization event between a tetraploid and a diploid Helianthus species,followed by chromosome doubling of the hybrid,which occurred approximately 2 million years ago.Moreover,we iden-tied more copies of actively expressed genes involved in inulin metabolism and showed that these genes may still be undergoing loss of function or sub-or neofunctionalization.These genomic resources will pro-mote further biological studies,breeding improvement,and industrial utilization of Helianthus crops.

CROP PROTECTION OPENS UP NEW ERA OF CONSERVATION AND UTILIZATION OF GREEN OPTIONS

China is the largest agricultural producer in the world.Reducing yield losses caused by pests is an important issue and major challenge for China,especially when confronting global climate change,biological invasions and declining agricultural biodiversity of recent decades.Wang et al.(this issue)summarized the impacts of changing climate on two staple crops in China,wheat and rice(https://doi.org/FASE-2021432).