Eucalyptus gunnii CCR and CAD2 promoters are active in lignifying cells during primary and secondary xylem formation in Arabidopsis thaliana

Cell-specific expression patterns of the Eucalyptus gunnii cinnamoyl coenzymeA reductase (EgCCR) and cinnamyl alcohol dehydrogenase (EgCAD2) promoters were analyzed by promoter-GUS histochemistry in the primary and secondary xylem tissues from floral stems and roots of Arabidopsis thaliana. Expression patterns indicated that the EgCCR and EgCAD2 genes were expressed in a coordinated manner in primary and secondary xylem tissues of the Arabidopsis floral stem and root. Both genes were expressed in all lignifying cells (vessel elements, xylem fibers and paratracheal parenchyma cells) of xylem tissues. The capacity for long-term monolignol production appeared to be related to the cell-specific developmental processes and biological roles of different cell types. Our results suggested that lignification of short-lived vessel elements was achieved by a two-step process involving (i) monolignol production by vessel elements prior to vessel programmed cell death and (ii) subsequent monolignol production by vessel-associated living paratracheal parenchyma cells following vessel element cell death. EgCCR and EgCAD2 gene expression patterns suggested that the process of xylem cell lignification was similar in both primary and secondary xylem tissues in Arabidopsis floral stems and roots.     

巴西橡胶树HbMYB52基因的克隆及其在拟南芥中的表达

为揭示Hb MYB52在巴西橡胶树(Hevea brasiliensis)木材发育过程中的功能,从其转录组中分离克隆到1个MYB转录因子G21亚组成员基因,命名为Hb MYB52,开放阅读框为726 bp,编码242个氨基酸的蛋白,在木质部中高度表达。在拟南芥(Arabidopsis thaliana)中过表达Hb MYB52,虽未改变转基因植株株型,但植株维管束间纤维细胞壁明显增厚,同时抑制了木质纤维、导管次生壁形成。转基因拟南芥株系3和株系6中纤维素和木质素含量减少,相应各组分合成的关键酶基因的表达量也不同程度下降;株系8产生了木质素异位沉积,且木质素合成关键酶基因表达活跃。因此,推测Hb MYB52参与了植物次生壁形成调控,在拟南芥次生壁形成中可能发挥了双重功能:一方面负调控维管束次生壁形成以及各组分的生物合成,另一方面具有促进束间纤维次生壁增厚的作用。     

Four mismatch repair paralogues coexist in Arabidopsis thaliana : AtMSH2, AtMSH3, AtMSH6-1 and AtMSH6-2

By using degenerate oligonucleotides based on the sequence homology between known MutS homologues, three MSH cDNAs belonging to the MSH2, MSH3 and MSH6 families, as defined in eukaryotes, have been isolated from Arabidopsis thaliana (ecotype Columbia). Genomic sequences for two of these genes (AtMSH2 and AtMSH6-2) were also isolated and determined, whereas the genomic sequence of AtMSH3 was obtained through the Arabidopsis sequencing project, as was the sequence of a second, distinct AtMSH6 homologue (AtMSH6-1). Comparative analysis of the AtMSH2 Landsberg erecta genomic sequence (reported here) and the previously described AtMSH2 Columbia allele revealed several polymorphisms, including the presence of a small, transposon-like element in the 3′ untranscribed region of the former allele. Arabidopsis is the first organism to show such divergence of two AtMSH6 genes; the divergence is strongly supported by sequence data and phylogenetic analysis. Southern analysis revealed that the three genes we have isolated exist as single copies, and genetic mapping indicated that AtMSH2 and AtMSH6-2 both reside on chromosome III. Finally, expression of these three genes could only be observed in suspensions of A. thaliana cells. Such a cell suspension divides actively after subculture, and the AtMSH genes are most strongly expressed at this stage. Received: 23 February 1999 / Accepted: 5 May 1999     

巴西橡胶树HbSUT3和HbSUT5 mRNA在嫩茎和中脉中的原位杂交分析

为研究巴西橡胶树(Hevea brasiliensis)中HbSUT3和HbSUT5基因的功能,采用地高辛标记的RNA探针与橡胶树嫩茎和中脉两种组织切片分别进行RNA原位杂交,对这2种SUT基因在组织中的表达区域与表达特点进行了分析。结果表明,在橡胶树嫩茎中,两个SUT基因主要在树皮的韧皮部和皮层细胞中表达;在中脉中,两个SUT基因在除木质部导管系统外的其它部位均有表达;HbSUT3基因在嫩茎和中脉中的表达量相近,而HbSUT5基因在嫩茎中的表达量远高于中脉。这些揭示HbSUT3和HbSUT5基因可能广泛参与韧皮部装载、蔗糖运输与库细胞供给等活动,同时两个SUT基因也存在功能分化。     

Chromosomal Mapping ofTmp(Emp1),Xmp(Emp2), andYmp(Emp3), Genes Encoding Membrane Proteins Related toPmp22

We have recently characterized a novel mammalian gene family, encoding membrane glycoproteins with four trans-membrane domains. This gene family includes the previously studiedPMP22,which is involved in the Charcot–Marie–Tooth neuropathy, and three novel genes:TMP, XMP,andYMP(HGMW-approved symbolsEMP1, EMP2andEMP3,respectively). TheTmp(tumor-associated membrane protein) gene was isolated from a c-mycinduced mouse brain tumor and is expressed in several highly proliferative cell types. We have now isolated cDNAs of the mouseXmpandYmpgenes and determined the chromosomal localization of mouseTmp, Xmp,andYmp. Tmpwas mapped to mouse chromosome 6,Xmpwas mapped to chromosome 16, andYmpwas mapped to chromosome 7.TmpandYmpmap to paralogous chromosomal regions, whereasXmpmaps to a chromosomal region that is putatively paralogous to a region on chromosome 11, to whichPmp22was previously mapped. These data suggest that this family of membrane glycoproteins evolved as a result of chromosomal duplications.     

海岛棉GbHCT13基因的功能验证

该研究利用海岛棉‘新海21’和陆地棉ND203以及模式植物拟南芥,通过转基因及荧光定量检测等方法探究海岛棉GbHCT13基因(GenBank 登录号MW048849)在纤维发育中的功能。结果显示：(1)成功构建重组载体pCAMBIA3301 GbHCT13,经农杆菌介导法转化、除草剂抗性基因筛选、荧光定量检测方法鉴定获得转GbHCT13基因拟南芥T₃代植株4株;qRT PCR检测表明,转基因植株中GbHCT13基因表达量较野生型极显著增加。(2)转基因拟南芥过表达GbHCT13基因使植株同一时期的生长较野生型旺盛,株形、叶片数、抽薹数和茎秆表皮毛数量均与野生型存在差异;组织化学分析发现,转GbHCT13基因的拟南芥较野生型茎秆初生木质部生长活跃,导管增粗,次生木质部导管细胞壁横截面积变大,但髓质细胞无明显变化;过表达GbHCT13使拟南芥中木质素合成途径基因发生不同程度改变,其中CAD、CCoAOMT、PAL和4CL与GbHCT13基因的表达呈正相关。(3)经大田筛选、分子鉴定,成功获得转GbHCT13基因棉花植株3株;转GbHCT13基因棉花的棉纤维伸长率增加,纤维强度增大;沉默GbHCT13基因使棉花植株木质素含量降低,茎秆表皮毛数量减少,木质部导管细胞数量减少,导管细胞壁中木质素沉积量降低,而棉株并未发生株高上的明显矮化现象,且木质素合成通路中的CAD、CCoAOMT、CCR、PAL 4个基因的表达均呈降低趋势,说明抑制GbHCT13使得棉花生长代谢受阻,影响纤维发育起始。研究表明,GbHCT13基因能影响棉花植株中木质素合成从而调控纤维的生长发育,其功能与GbHCT13基因在模式植物拟南芥中的基本一致。     

The Populus homeobox gene ARBORKNOX1 reveals overlapping mechanisms regulating the shoot apical meristem and the vascular cambium

Secondary growth is supported by a dividing population of meristematic cells within the vascular cambium whose daughter cells are recruited to differentiate within secondary phloem and xylem tissues. We cloned a Populus Class 1 KNOX homeobox gene, ARBORKNOX1 (ARK1), which is orthologous to Arabidopsis SHOOT MERISTEMLESS (STM). ARK1 is expressed in the shoot apical meristem (SAM) and the vascular cambium, and is down-regulated in the terminally differentiated cells of leaves and secondary vascular tissues that are derived from these meristems. Transformation of Populus with either ARK1 or STM over-expression constructs results in similar morphological phenotypes characterized by inhibition of the differentiation of leaves, internode elongation, and secondary vascular cell types in stems. Microarray analysis showed that 41% of genes up-regulated in the stems of ARK1 over-expressing plants encode proteins involved in extracellular matrix synthesis or modification, including proteins involved in cell identity and signaling, cell adhesion, or cell differentiation. These gene expression differences are reflected in alterations of cell wall biochemistry and lignin composition in ARK1 over-expressing plants. Our results suggest that ARK1 has a complex mode of action that may include regulating cell fates through modification of the extracellular matrix. Our findings support the hypothesis that the SAM and vascular cambium are regulated by overlapping genetic programs. Electronic Supplementary Material Supplementary material is available for this article at This work was supported by the USDA Forest Service and USDA NRI Grant 2003-00664 to AG, and a grants from the U.S. Department of Energy, Office of Science, Biological and Environmental Research Carbon Sequestration Program to AG and SD.     

The Role of ABI3 and FUS3 Loci in Arabidopsis thaliana on Phase Transition from Late Embryo Development to Germination

Arabidopsis abi3 and fus3 mutants are defective in late embryo development and their embryos show precocious growth. To understand the function and role of ABI3 and FUS3, we analyzed expression patterns of genes which were normally activated during late embryo development and germination in these mutants. Using the differential display method, both upregulated and downregulated genes were observed in immature siliques of the abi3 fus3 double mutant. Four clones having more abundant expression in the abi3 fus3 double mutant than in wild type were isolated. These genes were activated during wild-type germination, suggesting that some genes that are activated during wild-type germination are precociously activated in the abi3 fus3 mutant during late embryo development. Also, genes that were activated during wild-type germination were isolated and their expression patterns during late embryo development in the wild type and in abi3, fus3, and abi3 fus3 mutants were analyzed. Sixteen such clones were found, and 11 of these showed derepression or precocious activation of gene expression in the mutants. These results indicate that ABI3 and FUS3 negatively regulate a particular set of genes during late embryo development. We also showed that immature fus3 siliques accumulated one-third of the wild-type level of abscisic acid (ABA), but mature fus3 siliques accumulated ABA at a level comparable to that in the wild type. The possible mechanisms of controlling developmental timing in late embryo development as well as collaborative and distinct roles of ABI3 and FUS3 are discussed.     

Characterization of a novel DNA damage-inducible gene of Saccharomyces cerevisiae , DIN7 , which is a structural homolog of the RAD2 and RAD27 DNA repair genes

A number of DNA damage-inducible genes (DIN) have been identified in Saccharomyces cerevisiae. In the present study we describe isolation of a novel gene, Din7, the expression of which is induced by exposure of cells to UV light, MMS (methyl methanesulfonate) or HU (hydoxyurea). The DNA sequence of DIN7 was determined. By comparison of the predicted Din7 amino acid sequence with those in databases we found that it belongs to a family of proteins which includes S. cerevisiae Rad2 and its Schizosaccharomyces pombe and human homologs Rad13 and XPGC; S. cerevisiae Rad27 and its S. pombe homolog Rad2, and S. pombe Exo I. All these proteins are endowed with DNA nuclease activity and are known to play an important function in DNA repair. The strongest homology to Din7 was found with the Dhs1 protein of S.␣cerevisiae, the function of which is essentially unknown. The expression of the DIN7 gene was studied in detail using a DIN7-lacZ fusion integrated into a chromosome. We show that the expression level of DIN7 rises during meiosis at a time nearly coincident with commitment to recombination. No inducibility of DIN7 was found after treatment with DNA-damaging agents of cells bearing the rad53-21 mutation. Surprisingly, a high basal level of DIN7 expression was found in strains in which the DUN1 gene was inactivated by transposon insertion. We suggest that a form of Dun1 may be a negative regulator of the DIN7 gene expression. Received: 30 May 1996 / Accepted: 26 September 1996