Karyotype Stability and Unbiased Fractionation in the Paleo-Allotetraploid Cucurbita Genomes

The Cucurbita genus contains several economically important species in the Cucurbitaceae family. Here, we report high-quality genome sequences of C. maxima and C. moschata and provide evidence supporting an allotetraploidization event in Cucurbita. We are able to partition the genome into two homoeologous subgenomes based on different genetic distances to melon, cucumber, and watermelon in the Benincaseae tribe. We estimate that the two diploid progenitors successively diverged from Benincaseae around 31 and 26 million years ago （Mya）, respectively, and the allotetraploidization happened at some point between 26 Mya and 3 Mya, the estimated date when C. maxima and C. moschata diverged. The subgenomes have largely maintained the chromosome structures of their diploid progenitors. Such long-term karyotype stability after polyploidization has not been commonly observed in plant polyploids. The two subgenomes have retained similar numbers of genes, and neither subgenome is globally dominant in gene expression. Allele-specific expression analysis in the C. maxima ×C. moschata interspecific F1 hybrid and their two parents indicates the predominance of trans-regulatory effects underlying expression divergence of the parents, and detects transgressive gene expression changes in the hybrid correlated with heterosis in important agronomic traits. Our study provides insights into polyploid genome evolution and valuable resources for genetic improvement of cucurbit crops.

A Detected Case of Avian Influenza H9N2 from Influenza-Like Illness Surveillance--Hunan Province, 2020

Jishou Municipal Center for Disease Control and Prevention(Jishou CDC)received a phone call at 7:30 a.m.on April 24,2020 from Xiangxi Tujia and Miao Autonomous Prefectural CDC(Xiangxi CDC)that avian influenza A/H9N2 virus was detected by quantitative reverse transcription-polymerase chain reaction(RT-PCR)from the throat swab sample of an influenza-like illness in an outpatient in the Xiangxi Traditional Chinese Medicine Hospital.

GmYSL7 controls iron uptake,allocation,and cellular response of nodules in soybean

Iron(Fe)is essential for DNA synthesis,photosynthesis and respiration of plants.The demand for Fe substantially increases during legumesrhizobia symbiotic nitrogen fixation because of the synthesis of leghemoglobin in the host and Fecontaining proteins in bacteroids.However,the mechanism by which plant controls iron transport to nodules remains largely unknown.Here we demonstrate that GmYSL7 serves as a key regulator controlling Fe uptake from root to nodule and distribution in soybean nodules.GmYSL7 is Fe responsive and GmYSL7 transports iron across the membrane and into the infected cells of nodules.Alterations of GmYSL7 substantially affect iron distribution between root and nodule,resulting in defective growth of nodules and reduced nitrogenase activity.GmYSL7 knockout increases the expression of GmbHLH300,a transcription factor required for Fe response of nodules.Overexpression of GmbHLH300 decreases nodule number,nitrogenase activity and Fe content in nodules.Remarkably,GmbHLH300 directly binds to the promoters of ENOD93 and GmLbs,which regulate nodule number and nitrogenase activity,and represses their transcription.Our data reveal a new role of GmYSL7 in controlling Fe transport from host root to nodule and Fe distribution in nodule cells,and uncover a molecular mechanism by which Fe affects nodule number and nitrogenase activity.