Rhizobia interact with host legumes to induce the formation of nitrogen-fixing nodules,which is very important in agriculture and ecology.The development of nitrogen-fixing nodules is stringently regulated by host plants and rhizobial symbionts.In our previous work,a new Sinorhizobium meliloti LysR regulator gene(lsrB)was identified to be essential for alfalfa nodulation.However,how this gene is involved in alfalfa nodulation was not yet understood.Here,we found that this gene was associated with prevention of premature nodule senescence and abortive bacteroid formation.Heterogeneous deficient alfalfa root nodules were induced by the in-frame deletion mutant of lsrB(lsrB1-2),which was similar to the plasmid-insertion mutant,lsrB1.Irregular senescence zones earlier appeared in these nodules where bacteroid differentiation was blocked at different stages from microscopy observations.Interestingly,oxidative bursts were observed in these nodules by DAB staining.The decreased expression of lipopolysaccharide core genes(lpsCDE)was correspondingly determined in these nodules.S.meliloti lipopolysaccharide is required for suppression of oxidative bursts or host cell defense.These findings demonstrate that the S.meliloti lsrB gene is involved in alfalfa root nodule development and bacteroid differentiation by suppressing oxidative bursts or defense responses in host cells.
小肽分子是植物细胞分化、器官形成和生物防御的重要信号分子.通过分析大豆全基因组DNA序列,发现大量的基因编码小肽前体即小多肽分子.到目前为止,对这些小多肽分子的特征以及功能知之甚少.本文系统地分析了公共数据库中的大豆转录组数据,鉴定了212个在根瘤中增强表达的小多肽基因.其中79个基因属于38个多基因家族,而另外133个基因不属于任何基因家族.在38个基因家族中,有10个基因家族只出现在豆科植物中,另外28个也出现在模式植物拟南芥中.在大豆中,最大的一个基因家族是伤流诱导的小多肽(wound-induced small protein,WIP)基因家族,由38个成员组成,其中一半左右的基因在大豆固氮根瘤中增强表达.我们进一步分析了蒺藜苜蓿、百脉根、拟南芥和水稻中的WIP同源基因,发现部分基因也在根瘤中增强表达或者受病原菌诱导表达.二级结构分析显示,WIP小多肽前体均含有一个DUF3774结构域,其中包含2个跨膜疏水区域,多数分子具有N-端信号肽序列.我们选取了2个大豆WIP基因进行亚细胞定位分析,发现WIP小多肽定位于细胞膜上.有趣的是,34个大豆WIP基因成簇分布在3条染色体上,与目前发现的其他小多肽基因家族的分散分布(如CLE)完全不同.在6,12和13号染色体上分别分布有11,12和11个WIP基因.而在12号染色体上的WIP同源基因则位于13号染色体上,二者呈对应关系.而6号染色体上的WIP基因相互之间同源性最高,且只与12号染色体上的基因具有较高的同源性.因此,可以推测,在大豆基因组中WIP基因可能起源13号染色体,通过染色体复制扩散至12号染色体,再扩散到6号染色体.而在拟南芥和水稻基因组中,半数以上的WIP基因也分布在一条染色体上,且与大豆12和13号染色体上的WIP基因具有较高的同源性.因此,植物中WIP基因可能来源一个共同的祖先.
Small peptides function as key signals in processes,such as plant cell differentiation,organ development and defenses to biotic stresses.A large number of small peptide precursor genes have been predicted from the analysis of the soybean(Glycine max) whole genome DNA sequence.However,most of these genes have unknown characteristics and functions.In this report,we systemically searched for the gene families of small peptide precursors that are up-regulated in soybean nitrogen-fixing root nodules.We found 212 genes(encoding peptides shorter than 150 amino acids) that were up-regulated,and among them,79 genes belong to 38 multiple-gene families,but the other 133 genes are unique.Twenty-eight of 38 families are conserved in Arabidopsis,but the other 10 only exist in legumes.We also identified 16 out of the 38 members of the wound-induced polypeptide(WIP) gene family to be upregulated in nitrogen-fixing nodules.We further analyzed homologs of WIP genes in Medicago,Lotus,Arabidopsis and Oryza species and found that a few homologous genes from Medicago truncatula and Lotus japonicus were also upregulated in their nodules and some WIP genes were induced by specific fungal pathogens on soybean and rice.Structure prediction indicated that all WIP prepropeptides contain a conserved DUF3774 domain(including two hydrophobic regions) and most of them have an N-terminal signal sequence.Fluorescence microscopy analysis of two WIP prepropeptides fused to GFP revealed that these proteins are located on the plasma membrane of tobacco leaf cells.Interestingly,34 soybean WIP genes are clustered onto three soybean chromosomes,different from known peptide gene families(such as CLE).Among them,11 highly identical genes are aligned on the 6th chromosome,12 on the 12th,and 11 on the 13th chromosomes.Most of WIP genes from the 12th chromosome share the highest identities with their homologs on the 13th chromosome,suggesting that ancestral WIP genes could have originated from the 13th chromosome,then spread onto the 12th chromosome by chrom
