QTLs involved in the restriction of cucumber mosaic virus (CMV) long-distance movement in pepper

Partial restriction of cucumber mosaic virus (CMV) long-distance movement originating from the Capsicum annuum inbred line ’Vania’ was assessed in a doubled-haploid progeny using two screening methods: the first allowed one to assess the resistance of adult plants decapitated above the fourth leaf and inoculated on the third leaf using a common CMV strain, and the second allowed one to assess CMV resistance to long-distance movement on seedlings inoculated using an atypical CMV strain. For both resistance tests, the behavior of the F₁ hybrid between ’Vania’ and the susceptible line ’H3’ indicated that partial resistance is inherited as a dominant trait. Phenotypic data from the two screening methods were correlated but the one performed on seedlings was much more severe. A subset of 184 molecular markers well-distributed over the pepper genome was selected for QTL mapping using the composite interval mapping (CIM) method. A total of seven genomic regions, including one major effect and several minor effect QTLs, were shown to be associated with partial restriction of CMV long-distance movement. These results are compared with those already obtained in pepper and also in other solanaceous crops, potato and tomato. Received: 22 March 2001 / Accepted: 9 July 2001     

Two amino acids on 2a polymerase of<Emphasis Type="Italic">Cucumber mosaic virus</Emphasis> co-determine hypersensitive response on legumes

The hypersensitive response (HR) is one of the most important defense responses during the incompatible interaction between plant and pathogen. The viral determinant of HR on legumes induced byCucumber mosaic virus (CMV) was studied, and our previous results showed that 243 nucleotides on 2a polymerase gene of CMV were involved in the induction of HR on legumes. With further analysis of the nucleotides and amino acids in this region, the amino acids Phe and Ala at positions 631 and 641 in the 2a polymerase of CMV-Fny, a legume local necrotic strain, were specifically exchanged to Tyr and Ser, respectively and simultaneously, in the 2a polymerase of CMV-P1, a legume systemic infecting strain, and three point mutants were constructed. The point mutant Fny-F/Y (Phe631 to Tyr) induced large necrotic lesions instead of pinpoint lesions, and the size of lesions could enlarge from initial sites. The point mutant Fny-A/S (Ala641 to Ser) induced similar symptoms as CMV-Fny. The double-point mutant Fny-FA/YS (Phe631 to Tyr and Ala641 to Ser) infected the legumes systemically without HR. These data indicate that the induction of HR on legumes is co-determined by two amino acids at positions 631 and 641 in CMV 2a polymerase.     

Comparative Transcriptome Analyses Reveal Genes Related to Spine Development in Cucumber (<i>Cucumis sativus</i>)

Fruit spine is an important quality trait of cucumber. To better understand the molecular basis of cucumber spine development and function, RNA-Seq was performed to identify differentially expressed genes (DEGs) in fruit spines of different development stages, namely, 8 days before anthesis (SpBA8), anthesis (SpA) and 8 days after anthesis (SpAA8). Stage-wise comparisons obtained 2,259 (SpBA8 vs. SpA), 4,551 (SpA vs. SpAA8), and 5,290 (SpBA8 vs. SpAA8) DEGs. All the DEGs were classified into eight expression clusters by trend analysis. Among these DEGs, in addition to the Mict, Tril, CsTTG1, CsMYB6, NS, and Tu genes that have been reported to regulate fruit spine formation, we found that the CsHDG11, CsSCL8, CsSPL8, CsZFP6 and CsZFP8 may also be involved in spine development in cucumber. Our study provides a theoretical basis for further research on molecular mechanisms of spine development in cucumber.     

Differential impact of low temperature on fatty acid unsaturation and lipoxygenase activity in figleaf gourd and cucumber roots

Previous studies show that low temperature strongly induces suberin layers in the roots of chilling-sensitive cucumber plants, while in contrast, low temperature produces a much weaker induction of suberin layers in the roots of the chilling-tolerant figleaf gourd [S.H. Lee, G.C. Chung, S. Steudle, Gating of aquaporins by low temperature in roots of chilling-sensitive cucumber and -tolerant figleaf gourd, J. Exp. Bot. 56 (2005) 985-995; S.H. Lee, G.C. Chung, E. Steudle, Low temperature and mechanical stresses differently gate aquaporins of root cortical cells of chilling-sensitive cucumber and figleaf gourd, Plant Cell Environ. (2005) in press; S.J. Ahn, Y.J. Im, G.C. Chung, B.H. Cho, S.R. Suh, Physiological responses of grafted-cucumber leaves and rootstock roots affected by low root temperature, Scientia Hort. 81 (1999) 397-408]. Here, the effect of low temperature on fatty acid unsaturation and lipoxygenase activity was examined in cucumber and figleaf gourd. The double bond index demonstrated that membrane lipid unsaturation shows hyperbolic saturation curve in figleaf gourd roots while a biphasic response in cucumber roots to low temperature. In figleaf gourd, the hyperbolic response in the double bond index was primarily due to accumulation of linolenic acid. Chilling stress also significantly induced lipoxygenase activity in figleaf gourd roots. These results suggest that the degree of unsaturation of root plasma membrane lipids correlates positively with chilling-tolerance. Therefore, studies that compare the effects of chilling on cucumber and figleaf gourd may provide broad insight into stress response mechanisms in chilling-sensitive and chilling-tolerant plants. Furthermore, these studies may provide important information regarding the relationship between lipid unsaturation and lipoxygenase function/activity, and between lipoxygenase activity and water channeling during the response to chilling stress. The possible roles of these processes in chilling tolerance are discussed.     

Oxidative DNA damage in cucumber cotyledons irradiated with ultraviolet light

DNA was isolated from the cotyledons of cucumber seedlings irradiated with ultraviolet (UV)-C (254 nm) or UV-B+UV-A (280–360 nm; maximum energy at 312 nm) at various fluence rates and durations. Following enzymatic hydrolysis of DNA, the content of 8-hydroxy-2-deoxyguanosine [(8-OHdG), 8-oxo-7,8-dihydro-2-deoxyguanosine], a well-established biomarker closely identified with carcinogenesis and aging in animal cells, was determined using a high-performance liquid chromatograph equipped with an electrochemical detector. The levels of 8-OHdG increased with UV-C and UV-B irradiation in a fluence-dependent manner. This increase was also observed in etiolated cotyledons that had been excised from dark-grown cucumber seedlings and then cultured in vitro under UV light: monochromatic UV light at 270 nm or 290 nm increased the 8-OHdG level considerably, while UV at wavelengths above 310 nm had only small effects. In situ detection of H₂O₂ and quantification of H₂O₂ in plant extracts revealed that H₂O₂ accumulated in cotyledons irradiated with UV light. These results suggest that UV irradiation induces oxidative DNA damage in plant cells.     

Contribution of Mutation and RNA Recombination to the Evolution of a Plant Pathogenic RNA

The nucleotide sequence of 17 variants of the satellite RNA of cucumber mosaic virus (CMV-satRNA) isolated from field-infected tomato plants in the springs of 1989, 1990, and 1991 was determined. The sequence of each of the 17 satRNAs was unique and was between 334 and 340 nucleotides in length; 57 positions were polymorphic. There was much genetic divergence, ranging from 0.006 to 0.141 nucleotide substitutions per site for pairwise comparisons, and averaging 0.074 for any pair. When the polymorphic positions were analyzed relative to a secondary structure model proposed for CMV-satRNAs, it was found that there were significantly different numbers of changes in base-paired and non–base-paired positions, and that mutations that did not disrupt base pairing were preferred at the putatively paired sites. This supports the concept that the need to maintain a functional structure may limit genetic divergence of CMV-satRNA. Phylogenetic analyses showed that the 17 CMV-satRNA variants clustered into two subgroups, I and II, and evolutionary lines proceeding by the sequential accumulation of mutations were apparent. Three satRNA variants were outliers for these two phylogenetic groups. They were shown to be recombinants of subgroup I and II satRNAs by calculating phylogenies for different molecular regions and by using Sawyer's test for gene conversion. At least two recombination events were required to produce these three recombinant satRNAs. Thus, recombinants were found to be frequent (∼17%) in natural populations of CMV-satRNA, and recombination may make an important contribution to the generation of new variants. To our knowledge this is the first report of data allowing the frequency of recombinant isolates in natural populations of an RNA replicon to be estimated. Received: 14 May 1996 / Accepted: 17 July 1996     

利用植物激素调控嫁接形成的初步研究

利用黄瓜（Ｃｕｃｕｍ ｉｓｓａｔｉｖｕｓ）试管苗进行离体茎段自体嫁接,研究ＩＢＡ 和６－ＢＡ 对嫁接形成的影响时发现：进行离体茎段嫁接时,用试管苗茎段可简化嫁接过程,减少污染。嫁接茎段的颜色变化、不定根发生和愈伤组织形成与激素浓度有关。植物激素通过影响砧木和接穗间维管束桥形成的时间和数目调控嫁接组合的发育。在作者的实验中,最佳的激素条件是：在接穗培养基中加ＩＢＡ １．２ ｍ ｇ／Ｌ,在接穗和砧木培养基中加６－ＢＡ ０．３ ｍ ｇ／Ｌ。     

水杨酸对黄瓜叶片抗氧化剂酶系的调节作用

分析了水杨酸（ＳＡ）对黄瓜（ＣｕｃｕｍｉｓｓａｔｉｖｕｓＬ．）叶片抗氧化剂酶系活性及活性氧水平的调节作用。不同浓度的ＳＡ（０．５ｍｍｏｌ／Ｌ、１ｍｍｏｌ／Ｌ、２．５ｍｍｏｌ／Ｌ、５ｍｍｏｌ／Ｌ）均能显著地提高被处理叶片超氧化物歧化酶（ＳＯＤ）和过氧化物酶（ＰＯＤ）活性,而且还能诱导同株的非处理叶片中ＳＯＤ和ＰＯＤ活性增加。用１ｍｍｏｌ／ＬＳＡ处理第一片真叶,在处理后６～７２ｈ,ＰＯＤ活性增加了２２％～６７％,同株非处理的第二片真叶ＰＯＤ活性增加了１４％～８６％,但是,在ＳＡ处理后３ｈ之前以及处理９６ｈ之后,ＰＯＤ活性没有变化。ＳＡ能够显著降低超氧物阴离子含量和提高过氧化氢水平,但它对过氧化氢酶（ＣＡＴ）活性的抑制作用很弱,表明ＳＡ提高体内过氧化氢含量的原因主要是通过提高ＳＯＤ活性而不是抑制ＣＡＴ活性。同工酶分析表明,ＳＡ不能诱导新的ＳＯＤ同工酶,但可以诱导新的ＰＯＤ同工酶。     

QTLs for a component of partial resistance to cucumber mosaic virus in pepper: restriction of virus installation in host-cells

 Ninety four doubled-haploid (DH) lines obtained from the F₁ between Perennial, a cucumber mosaic virus (CMV)-partially resistant Capsicum annuum line, and Yolo Wonder, a CMV-susceptible C. annuum line, were analysed with 138 markers including mostly RFLPs and RAPDs. Clustering of RAPD markers was observed on five linkage groups of the intraspecific linkage map. These clusters could correspond to the centromeric regions of pepper chromosomes. The same progenies were evaluated for restriction of CMV installation in pepper cells in order to map quantitative trait loci (QTLs) controlling CMV resistance. This component of partial resistance to CMV was quantitatively assessed using a CMV strain that induced necrotic local lesions on the inoculated leaves. The number of local lesions gave an estimation of the density of the virus-infection sites. Genotypic variance among the DH lines was highly significant for the number of local lesions, and heritability was estimated to be 0.94. Using both analysis of variance and non-parametric tests, three genomic regions significantly affecting CMV resistance were detected on chromosomes Noir, Pourpre and linkage group 3, together explaining 57% of the phenotypic variation. A digenic epistasis between one locus that controlled significant trait variation and a second locus that by itself had no demonstrable effect on the trait was found to have an effect on CMV resistance. For each QTL, the allele from Perennial was associated with an increased resistance. Implications of QTL mapping in marker-based breeding for CMV resistance are discussed. Received: 16 September 1996     

Redox thermodynamics, acid-base equilibria and salt-induced effects for the cucumber basic protein. General implications for blue-copper proteins

 The reduction potential of the basic blue-copper protein from cucumber peels (CBP) was determined through voltammetric techniques in different conditions of temperature, pH and ionic composition of the medium. The most notable properties of CBP include a positive entropy change upon reduction, a low-pH protonation and detachment of a metal-binding histidine in the reduced protein, and specific binding interactions with a number of anions present in common laboratory buffers, which influence to some extent the redox thermodynamics. The enthalpy and entropy changes accompanying reduction of the Cu(II) center were compared with those for other blue-copper proteins and correlated with spectroscopic data, structural properties and theoretical calculations. This allows some general considerations to be offered regarding the determinants of the reduction potential in this protein class. It emerges, in line with previous studies of the electronic structure of blue-copper sites, that the enthalpic contribution to the reduction potential is mainly modulated by the metal-binding interactions in the trigonal N₂S ligand set, and particularly by the Cu-cysteinate bond, while the entropy term is mainly affected by solvation properties and possibly by the weak axial bond to copper. The role of solvent exposure of the metal site in the active-site protonations in reduced blue-copper proteins is discussed. Finally, it is shown that the Nernst-Debye-Huckel model qualitatively accounts for the ionic strength dependence of the reduction potential. Received: 20 December 1996 / Accepted: 26 March 1997