Dear Editor,Since the first plant receptor-like kinase(RLK)geneZmPK1 was cloned from Zea mays in 1990(Walker and Zhang,1990),this large gene family has been extensively studied and shown to play crucial roles in growth,development,and immunity(Tang et al.,2017).RLKs are widespread in the plant kingdom.However,biological functions of most RLKs remain largely elusive(Dievart et al.,2020).Given RLKs share a conserved monophyletic RLK/Pelle kinase domain,RLKs in several model plants are classified into distinct families by extracellular domains(Shiu and Bleecker,2001).However,independent domain shuffling in specific lineages drives the origin of novel families,which raises a question what is the landscape of RLKs across the entire plant kingdom?

Receptor-like kinases(RLKs)are the most numerous signal transduction components in plants and play important roles in determining how different plants adapt to their ecological environments.Research on RLKs has focused mainly on a small number of typical RLK members in a few model plants.There is an ur-gent need to study the composition,distribution,and evolution of RLKs at the holistic level to increase our understanding of how RLKs assist in the ecological adaptations of different plant species.In this study,we collected the genome assemblies of 528 plant species and constructed an RLK dataset.Using this dataset,we identified and characterized 524 948 RLK family members.Each member underwent systematic topo-logical classification and was assigned a gene ID based on a unified nomenclature system.Furthermore,we identified two novel extracellular domains in some RLKs,designated Xiao and Xiang.Evolutionary anal-ysis of the RLK family revealed that the RLCK-ⅩⅦ and RLCK-Ⅻ-2 classes were present exclusively in di-cots,suggesting that diversification of RLKs between monocots and dicots may have led to differences in downstream cytoplasmic responses.We also used an interaction proteome to help empower data mining for inference of new RLK functions from a global perspective,with the ultimate goal of understanding how RLKs shape the adaptation of different plants to the environments/ecosystems.The assembled RLK data-set,together with annotations and analytical tools,forms an integrated foundation of multiomics data that is publicly accessible via the metaRLK web portal(http://metaRLK.biocloud.top).

植物小分子信号肽(small signaling peptides,SSPs)是一类蛋白长度小于 120 个氨基酸的小肽,作为新型信号分子在植物应答非生物逆境胁迫中发挥重要的作用.植物中含有千余种SSPs,多种多样的结构特点、修饰过程与不同受体的结合发挥其特异的功能,参与植物与环境之间的互作.挖掘鉴定植物SSPs功能基因,解析它们应答非生物逆境胁迫的调控机制,对增强植物抗性、改善植物生长具有重要的理论与实践意义.植物SSPs主要包括胞外非分泌型小肽、胞内非分泌型小肽、胞外翻译后修饰分泌型小肽和胞外富含半胱氨酸分泌型小肽四大类.介绍了四类植物SSPs的结构、特征;阐述了它们以SSP配体结合LRR-RLK受体激酶完成信号转导过程,以激活下游抗性基因表达为模式的调控机制;重点综述了它们在干旱、高温、盐渍、营养等非生物逆境胁迫应答中的生物学功能及调控机制.最后讨论了植物SSPs未来研究的方向和有待解决的问题,还对SSPs类生长调节剂的开发前景进行了展望,旨在为提高植物应对环境胁迫和实现农业可持续发展提供新的思路和路径.

Pollen hydration on dry stigmas is strictly regulated by pollen-stigma interactions in Brassicaceae.Although several related molec-ular events have been described,the molecular mechanism underlying pollen hydra-tion remains elusive.Multiple B-class pollen coat proteins(PCP-Bs)are involved in pollen hydration.Here,by analyzing the interactions of two PCP-Bs with three Arabidopsis thaliana stigmas strongly expressing S-domain receptor kinase(SD-RLK),we determined that SD-RLK28 directly interacts with PCP-Bβ.We investigated pollen hydration,pollen germination,pollen tube growth,and stigma receptivity in the sd-rlk28 and pcp-bβ mutants.PCP-Bβ acts in the pollen to regulate pollen hydration on stigmas.Loss of SD-RLK28 had no effect on pollen viability,and sd-rlk28 plants had normal life cycles without obvious defects.However,pollen hydration on sd-rlk28 stigmas was im-paired and pollen tube growth in sd-rlk28 pistils was delayed.The defect in pollen hydration on sd-rlk28 stigmas was independent of changes in reactive oxygen species levels in stigmas.These results indicate that SD-RLK28 functions in the stigma as a PCP-Bβ receptor to positively regulate pollen hydration on dry stigmas.

Cell-surface-localized leucine-rich-repeat receptor-like kinases(LRR-RLKs)are crucial for plant immunity.Most LRR-RLKs that act as receptors directly recognize ligands via a large extracellular domain(ECD),whereas LRR-RLK that serve as regulators are relatively small and contain fewer LRRs.Here,we identified LRR-RLK regulators using high-throughput tobacco rattle virus(TRV)-based gene silencing in the model plant Nicotiana ben-thamiana.We used the cell-death phenotype caused by INF1,an oomycete elicitin that induces pattern-triggered immunity,as an indicator.By screening 33 small LRR-RLKs(≤6 LRRs)of unknown function,we identified ELICITIN INSENSITIVE RLK 1(NbEIR1)as a positive regulator of INF1-induced immunity and oomycete resistance.Nicotiana benthamiana mutants of eir1 generated by CRISPR/Cas9-editing showed significantly com-promised immune responses to INF1 and were more vulnerable to the oomycete pathogen Phy-tophthora capsici.NbEIR1 associates with BRI1-ASSOCIATED RECEPTOR KINASE 1(NbBAK1)and a downstream component,BRASSINOSTEROID-SIGNALING KINASE 1(NbBSK1).NbBSK1 also contributes to INF1-induced defense and P.capsici resistance.Upon INF1 treatment,NbEIR1 was released from NbBAK1 and NbBSK1 in vivo.Moreover,the silencing of NbBSK1 compromised the association of NbEIR1 with NbBAK1.We also showed that NbEIR1 regulates flg22-induced im-munity and associates with its receptor,FLAGELLIN SENSING 2(NbFLS2).Collectively,our results sug-gest that NbEIR1 is a novel regulatory element for BAK1-dependent immunity.NbBSK1-NbEIR1 asso-ciation is required for maintaining the NbEIR1/NbBAK1 complex in the resting state.

FERONIA(FER)类受体蛋白激酶是CrRLK1L(Catharanthus roseus RLK1-like)激酶亚家族成员,在植物受精、细胞伸长、顶端生长以及非生物胁迫响应等方面起重要作用.本研究克隆了两个花生(Arachis hypogaea)FER类受体蛋白激酶基因AhFER1和AhFER2,它们的完整编码序列(CDS)和相应基因组DNA序列完全一致,说明AhFER1和AhFER2基因编码区均无内含子,分别包括2655和2640 bp的完整开放阅读框,编码的蛋白分别含885和880个氨基酸,分子量分别为99.58和98.96 kDa,等电点分别为6.5和6.22.生物信息学分析发现,AhFER1及AhFER2的氨基酸序列与其他植物FER蛋白均具有较高同源性,都包含malectin-like和蛋白激酶催化域两个保守结构域.AhFER1和AhFER2基因在花生幼苗的叶、茎和根中的表达水平有差异:AhFER1基因在叶中表达量最高,其次是根,茎中表达量最低;而AhFER2基因则在茎中表达量最高,其次是叶,表达量最低是根.干旱胁迫对花生茎和根中AhFER1基因的表达以及花生叶、茎和根中AhFER2基因的表达均无影响,但干旱胁迫显著增强花生叶中AhFER1基因的表达,说明AhFER1基因可能在花生叶响应干旱胁迫时起重要作用.

植物类受体激酶在植物生长发育及响应外界环境信号刺激中具有重要作用,为了进一步研究水稻类受体激酶OsBAKlL的功能,我们利用CRISPP/Cas9技术对该基因进行定点编辑.OsBAK1L定位在细胞膜上且该基因预测编码蛋白包含三个功能结构域:胞外LRR结构域、跨膜结构域及胞内激酶域.为了进一步理解该蛋白不同结构域上的功能,我们分别在胞外LRR结构域(Target l)和胞内激酶域(Target2)上设计该基因定点编辑靶点.将合成的靶位点序列插入入门载体CH,然后与表达载体Cas9进行重组.重组载体通过农杆菌介导方法转入野生型水稻9522中,2个构建分别获得26棵和12棵潮霉素抗性植株.通过对转基因植株的测序分析,找到了3棵和2棵序列发生变化的杂合T0代植株.T0代杂合植株自交分离分别获得T1代两靶位点处纯合子突变体,靶位点l处纯合子突变体株系缺失5个碱基,靶位点2处纯合子突变体株系插入1个碱基,均可造成该基因转录本翻译提前终止.该基因不同结构域上突变体的获得为进一步研究该基因功能提供了重要且稳定的遗传材料.

A normalized full-length cDNA library was constructed from the coralloid roots of Cycas debaoensis by the DSN (duplex-specific nuclease) normalization method combined with the SMART (Switching Mechanism At 5' end of the RNA Transcript) technique. The titer of the original cDNA library was about 1.5 × 106 cfu·mL-1 and the average insertion size was about 1 kb with a high recombination rate (97％). The 5011 high-quality expressed sequence tags (ESTs) were obtained from 5393 randomly picked cDNA clones. Clustering and assembly of ESTs resulted in 2984 unique sequences, consisting of 618 contigs and 2366 singlets. EST sequence annotation revealed that 2333 and 1901 unigenes were functionally anno-tated in the NCBI non-redundant database and Swiss-Prot protein database, respectively. Functional analysis demonstrated that 1495 (50.1％) unigenes were associated with 4082 Gene Ontology (GO) terms. A total of 847 unigenes were grouped into 22 Cluster of Orthologous Groups (COG) functional categories. Based on the EST dataset, 22 ESTs that encoded putative receptor-like protein kinase (RLK) genes were screened. Furthermore, a total of 94 simple sequence repeats (SSRs) were discovered, of which 20 loci were successfully amplified in C. debaoensis. This study is the first EST analysis for the coralloid roots of C. debaoensis and provides a valuable genomic resource for novel gene discovery, gene expression and comparative genomics, conservation and management studies as well as applications in C. debaoensis and related cycad species.

Plants employ receptor-like kinases (RLKs) and receptor-like proteins for rapid recognition of invading pathogens,and RLKs then transmit signals to receptor-like cytoplasmic kinases (RLCKs) to activate immune responses.RLKs are under fine regulation mediated by subcellular trafficking,which contributes to proper activation of plant immunity.In this study,we show that Arabidopsis thaliana RECEPTOR-LIKE KINASE 902 (RLK902) plays important roles in resistance to the bacterial pathogen Pseudomonas syringae,but not to the fungal powdery mildew pathogen Golovinomyces cichoracearum.RLK902 localizes at the plasma membrane and associates with ENHANCED DISEASE RESISTANCE 4 (EDR4),a protein involved in clathrin-mediated trafficking pathways.EDR4 and CLATHRIN HEAVY CHAIN 2 (CHC2) regulate the subcellular trafficking and accumulation of RLK902 protein.Furthermore,we found that RLK902 directly associates with the RLCK BRASSINOSTEROID-SIGNALING KINASE1 (BSK1),a key component of plant immunity,but not with other members of the FLAGELLIN SENSING 2 immune complex.RLK902 phosphorylates BSK1,and its Ser-230 is a key phosphorylation site critical for RLK902-mediated defense signaling.Taken together,our data indicate that EDR4 regulates plant immunity by modulating the subcellular traf ficking and protein accumulation of RLK902,and that RLK902 transmits immune signals by phosphorylating BSK1.

目的 克隆铁皮石斛Dendrobium 0fficinale类受体激酶(receptor-like kinase,RLK)基因,命名为DoRLK(GenBank注册号 ANC68272.1).方法 采用实时荧光定量 PCR(qRT-PCR)和 RACE技术获取基因全长;利用生物信息学软件预测蛋白的理化性质、结构域和亚细胞定位等分子特性;用软件DNASTAR6.0和MEGA 7.0分别进行氨基酸多序列比对和进化关系分析;借助定量PCR检测基因表达模式.结果 DoRLK基因cDNA全长1715bp,编码1条由423个氨基酸组成的多肽,相对分子质量 47800.88,等电点为9.47.DoRLK蛋白包含RLK蛋白家族的1个蛋白激酶结构域(85～370)和一个跨膜基序(250～270).DoRLK基因与多种植物 RLK基因相似性很高(43.62％～63.35％),与小兰屿蝴蝶兰、海枣、芦笋等植物亲缘关系较近.DoRLK基因具有组织表达特异性,其转录本在石斛根中表达量较高,分别为叶和茎中的2.22、2.75倍.结论 DoRLK基因的分子鉴定为进一步揭示RLK在铁皮石斛与环境互作中的功能奠定基础.