Patterns of transformation intensity on flax hypocotyls inoculated with Agrobacterium tumefaciens

Summary Cellular transformation intensities on flax (Linum usitatissimum) hypocotyl explants using disarmed Agrobacterium tumefaciens were investigated through various preculture durations, cocultivation durations and removal of epidermis. The expression of an intron-containing -glucuronidase (GUS) gene driven by CaMV 35S promoter served as a reporter for determination of transformed tissues on hypocotyls. The binary plasmid p35SGUSINT in octopine-type Agrobacterium strain GV2260 was used as the vector system. A prolonged cocultivation duration (5–7 days) resulted in a much higher transformation staining intensity (frequency * tissue area) than 2- or 3-day-cocultivation duration on hypocotyls variously precultured prior to inoculation. A high staining intensity on the two cut ends was obtained from nonprecultured hypocotyls. A reduction in intensity on the upper cut end of hypocotyls was observed with preculture times greater than 6 days. Peeled hypocotyls with a post-peeling preculture of 2 or 3 days had a high proportion of superficial area covered by transformed tissues after a 7 day-cocultivation duration. These results will help to improve the efficiency of recovery of transgenic plants by increasing the proportion of transformation in the regenerable tissues.     

The pTiC58 tzs gene promotes high-efficiency root induction by agropine strain 1855 of Agrobacterium rhizogenes

Root induction on flax (Linum usitatissimum L.) cotyledon explants by Agrobacterium rhizogenes strain 1855 is markedly increased by co-inoculation with disarmed A. tumefaciens strain LBA 4404 containing a plasmid carrying the tzs gene of pTiC58. Most of the roots (estimated to be more than 90%) were transformed. This effect is most likely due to the secretion of trans-zeatin by A. tumefaciens stimulating the division of plant cells making them more receptive to transformation by A. rhizogenes, although other explanations are possible. This observation supports the idea that the tzs gene, although not essential for transformation, may promote transformation. An obvious application for genetic engineering experiments involving transformation by A. rhizogenes, is to include a vir-induced tzs gene in the transformation system to help maximize transformation efficiency.     

The use of the phosphomannose isomerase gene as alternative selectable marker for Agrobacterium-mediated transformation of flax (Linum usitatissimum)

In order to meet the future requirement of using non-antibiotic resistance genes for the production of transgenic plants, we have adapted the selectable marker system PMI/mannose to be used in Agrobacterium-mediated transformation of flax (Linum usitatissimum L.) cv. Barbara. The Escherichia coli pmi gene encodes a phosphomannose isomerase (E.C. 5.1.3.8) that converts mannose-6-phosphate, an inhibitor of glycolysis, into fructose-6-phosphate (glycolysis intermediate). Its expression in transformed cells allows them to grow on mannose-selective medium. The Agrobacterium tumefaciens strain GV3101 (pGV2260) harbouring the binary vector pNOV2819 that carries the pmi gene under the control of the Cestrum yellow leaf curling virus constitutive promoter was used for transformation experiments. Transgenic flax plants able to root on mannose-containing medium were obtained from hypocotyl-derived calli that had been selected on a combination of 20 g L⁻¹ sucrose and 10 g L⁻¹ mannose. Their transgenic state was confirmed by PCR and Southern blotting. Transgene expression was detected by RT-PCR in leaves, stems and roots of in vitro grown primary transformants. The mean transformation efficiency of 3.6%, that reached 6.4% in one experiment was comparable to that obtained when using the nptII selectable marker on the same cultivar. The ability of T1 seeds to germinate on mannose-containing medium confirmed the Mendelian inheritance of the pmi gene in the progeny of primary transformants. These results indicate that the PMI/mannose selection system can be successfully used for the recovery of flax transgenic plants under safe conditions for human health and the environment.     

In Vivo and in Vitro Evidence for Biochemical Coupling of Reactions Catalyzed by Lysophosphatidylcholine Acyltransferase and Diacylglycerol Acyltransferase

Seed oils of flax (Linum usitatissimum L.) and many other plant species contain substantial amounts of polyunsaturated fatty acids (PUFAs). Phosphatidylcholine (PC) is the major site for PUFA synthesis. The exact mechanisms of how these PUFAs are channeled from PC into triacylglycerol (TAG) needs to be further explored. By using in vivo and in vitro approaches, we demonstrated that the PC deacylation reaction catalyzed by the reverse action of acyl-CoA:lysophosphatidylcholine acyltransferase (LPCAT) can transfer PUFAs on PC directly into the acyl-CoA pool, making these PUFAs available for the diacylglycerol acyltransferase (DGAT)-catalyzed reaction for TAG production. Two types of yeast mutants were generated for in vivo and in vitro experiments, respectively. Both mutants provide a null background with no endogenous TAG forming capacity and an extremely low LPCAT activity. In vivo experiments showed that co-expressing flax DGAT1-1 and LPCAT1 in the yeast quintuple mutant significantly increased 18-carbon PUFAs in TAG with a concomitant decrease of 18-carbon PUFAs in phospholipid. We further showed that after incubation of sn-2-[¹⁴C]acyl-PC, formation of [¹⁴C]TAG was only possible with yeast microsomes containing both LPCAT1 and DGAT1-1. Moreover, the specific activity of overall LPCAT1 and DGAT1-1 coupling process exhibited a preference for transferring ¹⁴C-labeled linoleoyl or linolenoyl than oleoyl moieties from the sn-2 position of PC to TAG. Together, our data support the hypothesis of biochemical coupling of the LPCAT1-catalyzed reverse reaction with the DGAT1-1-catalyzed reaction for incorporating PUFAs into TAG. This process represents a potential route for enriching TAG in PUFA content during seed development in flax.     

Variability in the composition of tissue-specific galactan from flax fibers

Tissue-specific galactan of sclerenchyma fibers, with cell walls of the gelatinous type, was examined in flax plants (Linum usitatissimum L.) of 23 various genotypes. The content and average degree of polymerization of side chains of galactan were estimated before its deposition into the cell wall. The variability of the analyzed parameters of tissue-specific galactan from flax fibers was high; within the same genotype, the scope of paratypic variability between replicates and years of research was comparable to variability between different genotypes. The average length of side chains in the studied samples ranged from 5 to 41 galactose residues. The average degrees of polymerization of galactan side chains in flax fibers was found to be discrete, which could be explained by block assemblage of the polymer in the Golgi apparatus.     

亚麻组织培养高频不定芽诱导体系

对适合南方地区冬季种植的纤用亚麻品种组织培养过程中基本培养基、激素配比、外植体材料的基因型和苗龄以及再生不定芽的生根条件进行了比较研究。结果表明,适合于亚麻白花品种组织培养的最佳培养基为YB1,不定芽诱导率可达98.50%。在此培养基上,白花、黑亚4号、K6531、K7697、HI026、HI045、I039和阿丽亚那下胚轴不定芽的诱导率分别为98.50%、98.50%、56.50%、42.47%、54.40%、0、27.13%和97.30%,平均出芽数为11.43、9.33、2.17、0.77、1.10、0、0.90和10.68。苗龄为7-10天的下胚轴最适于诱导不定芽,随苗龄增加,不定芽的诱导率呈下降趋势。RB5培养基最适于不定芽的生根,生根率达100%,平均生根数为15.3。实验还确定了亚麻对卡那霉素、氨苄青霉素和头孢霉素的抗性浓度阈值。     

Induction of lignans and phenolic compounds in cell culture of Linum album by culture filtrate of Fusarium graminearum

Cell suspension cultures of Linum album Kotschy ex Boiss. have been reported to produce anticancer podophyllotoxin and its related lignans. In the present study, we investigated the effect of culture filtrate of Fusarium graminearumon growth, and lignan and phenolic compounds in L. album cell culture. After 7 days of pre-culture, the cells were treated with 1% (v/v) of the culture filtrate. Cell growth was reduced, while phodophyllotoxin and lariciresinol production was stimulated reaching a maximum 0.0187 mg/g fresh weight (FW) and 0.0136 mg/g FW 5 days after the treatment, respectively. Also, our results provide evidence that the culture filtrate of F. graminearum can be effective on phenylalanine ammonia-lyase activity and phenolic compounds.     

Co-culture of arbuscular mycorrhiza-like fungi (Piriformospora indica and Sebacina vermifera) with plant cells of Linum album for enhanced production of podophyllotoxins: a first report

Cell suspension cultures of Linum album were developed from internode portions of in vitro germinated plant in Gamborg's B5 medium supplemented with 0.4 mg naphthalene acetic acid/l. The highest biomass was 8.5 g/l with podophyllotoxin and 6-methoxypodophyllotoxin at 29 and 1.9 mg/l, respectively after 12 d cultivation. Co-cultures of L. album cells with axenically cultivable arbuscular mycorrhiza-like fungi, Piriformospora indica and Sebacina vermifera, were established for the first time. These enhanced podophyllotoxin and 6-methoxypodophyllotoxin production by about four- and eight-fold, respectively, along with a 20% increase in biomass compared to the control cultures.     

Variation and evolution inLinum tenuifolium (Linaceae)

The phenetic variation inL. tenuifolium s.l. was assessed using multivariate analyses of 27 characters found to be variable within the species. These results are discussed and interpreted in the context of the reproductive biology, chromosome number and ecological responses of the taxa. Evidence suggests that both the self-compatible and tetraploid races were derived independently from a self-incompatible, diploid type. Although no taxonomic scheme is compatible with all of the evidence presented, the study supports a recent decision to recognize four taxa at subspecific level.