High-quality assembled and annotated genomes of Nicotiana tabacum and Nicotiana benthamiana reveal chromosome evolution and changes in defense arsenals

Nicotiana tabacum and Nicotiana benthamiana are widely used models in plant biology research.However,genomic studies of these species have lagged.Here we report the chromosome-level reference genome assemblies for N.benthamiana and N.tabacum with an estimated 99.5%and 99.8%completeness,respec-tively.Sensitive transcription start and termination site sequencing methods were developed and used for accurate gene annotation in N.tabacum.Comparative analyses revealed evidence for the parental origins and chromosome structural changes,leading to hybrid genome formation of each species.Interestingly,theantiviral silencinggenesRDR1,RDR6,DCL2,DCL3,andAGO2were lost from one or both subgenomes in N.benthamiana,while both homeologs were kept in N.tabacum.Furthermore,the N.benthamiana genome encodes fewer immune receptors and signaling components than that of N.tabacum.These find-ings uncover possible reasons underlying the hypersusceptible nature of N.benthamiana.We developed the user-friendly Nicomics(http:/lifenglab.hzau.edu.cn/Nicomics/)web server to facilitate better use of Nicotiana genomic resources as well as gene structure and expression analyses.

Multiple metal sources in polymetallic W-Sn ore deposits revealed by mercury stable isotopes

Granite-related W-Sn ore systems are commonly associated with coeval Pb-Zn mineralization. It remains unclear whether these metals are derived from the same sources or not. Mercury(Hg) is a common minor component in such systems. Hg isotopes undergo unique mass-independent fractionation(expressed as Δ^(199)Hg values), which is mainly generated during Hg photochemical reactions on Earth's surface and not affected by magmatic-hydrothermal processes, offering an excellent opportunity to trace metal sources in hydrothermal systems. We observed near-zero Δ^(199)Hg values in wolframite(-0.10‰ to0.08‰, n=11), and in skarn-(-0.17‰ to 0.12‰, n=48) and greisen-type(-0.12‰ to 0.10‰, n=11) bulk tin-tungsten ore from eight major ore deposits in South China. These values are identical to those of coeval highly evolved granites(-0.13‰ to 0.12‰,n=49), supporting that Hg in W-Sn ores were sourced from granite. However, sulfides(e.g., pyrite, chalcopyrite, arsenopyrite,galena, and sphalerite) in these deposits exhibit negative to near-zero Δ^(199)Hg values(-0.42‰ to 0.09‰, n=124), which indicates a contribution of Hg and by inference other metals from both Precambrian basement rocks(Δ^(199)Hg<0) and ore-related granites.The study demonstrates that multiple sources of metals were involved in the formation of the polymetallic W-Sn deposits, and further highlights that extraction of metals from basement rocks may be a critical control on the formation of economically important mineralization of base metal sulfides(e.g., Pb, Zn) in granite-related magmatic-hydrothermal systems.

The Ubiquitin E3 Ligase PUB17 Positively Regulates Immunity by Targeting a Negative Regulator, KH17, for Degradation

Ubiquitination is a post-translational modification that regulates many processes in plants.Several ubiquitin E3 ligases act as either positive or negative regulators of immunity by promoting the degradation of different substrates.StPUB17 is an E3 ligase that has previously been shown to positively regulate immunity to bacteria,fungi and oomycetes,including the late blight pathogen Phytophthora infestans.Silencing of StPUB17 promotes pathogen colonization and attenuates Cf4/avr4 cell death.Using yeast-2-hybrid and co-immunoprecipitation we identified the putative K-homology(KH)RNA-binding protein(RBP),StKH17,as a candidate substrate for degradation by StPUB17.StKH17 acts as a negative regulator of immunity that promotes P.infestans infection and suppresses specific immune pathways.A KH RBP domain mutant of StKH17(StKH17GDDG)is no longer able to negatively regulate immunity,indicating that RNA binding is likely required for StKH17 function.As StPUB17 is a known target of the ubiquitin E3 ligase,StPOB1,we reveal an additional step in an E3 ligase regulatory cascade that controls plant defense.

Oomycetes Seek Help from the Plant：Phytophthora infestans Effectors Target Host Susceptibility Factors

Plants have a sophisticated immune system to defend against a wide range of invaders,including insects,nematodes,bacteria,oomycetes,fungi,and viruses.Microbes may manipulate or suppress immunity by delivering effector proteins,either to the inside or outside of plant cells.Much attention has been focused on identifying the targets of effector proteins in the host and on characterizing how effector activities suppress immunity.