Fine mapping of loci involved with glucosinolate biosynthesis in oilseed mustard (Brassica juncea) using genomic information from allied species

Fine mapping of six seed glucosinolate QTL (J2Gsl1, J3Gsl2, J9Gsl3, J16Gsl4, J17Gsl5 and J3Gsl6) (Ramchiary et al. in Theor Appl Genet 116:77-85, 2007a) was undertaken by the candidate gene approach. Based on the DNA sequences from Arabidopsis and Brassica oleracea for the different genes involved in the aliphatic glucosinolate biosynthesis, candidate genes were amplified and sequenced from high to low glucosinolate Brassica juncea lines Varuna and Heera, respectively. Of the 20 paralogues identified, 17 paralogues belonging to six gene families were mapped to 12 of the 18 linkage groups of B. juncea genome. Co-mapping of candidate genes with glucosinolate QTL revealed that the candidate gene BjuA.GSL-ELONG.a mapped to the QTL interval of J2Gsl1, BjuA.GSL-ELONG.c, BjuA.GSL-ELONG.d and BjuA.Myb28.a mapped to the QTL interval of J3Gsl2, BjuA.GSL-ALK.a mapped to the QTL interval of J3Gsl6 and BjuB.Myb28.a mapped to the QTL interval of J17Gsl5. The QTL J9Gsl3 and J16Gsl4 did not correspond to any of the mapped candidate genes. The functionality and contribution of different candidate genes/QTL was assessed by allelic variation study using phenotypic data of 785 BC(4)DH lines. It was observed that BjuA.Myb28.a and J9Gsl3 contributed significantly to the base level glucosinolate production while J16Gsl4, probably GSL-PRO, BjuA.GSL-ELONG.a and BjuA.GSL-ELONG.c contributed to the C3, C4 and C5 elongation pathways, respectively. Three A genome QTL: J2Gsl1harbouring BjuA.GSL-ELONG.a, J3Gsl2 harbouring both BjuA.GSL-ELONG.c and BjuA.Myb28.a and J9Gsl3, possibly the 'Bronowski genes', were identified as most important loci for breeding low glucosinolate B. juncea. We observed two-step genetic control of seed glucosinolate in B. juncea mainly effected by these three A genome QTL. This study, therefore, provides clues to the genetic mechanism of 'Bronowski genes' controlling the glucosinolate trait and also provides efficient markers for marker-assisted introgression of low glucosinolate trait in B. juncea.

QTL analysis reveals context-dependent loci for seed glucosinolate trait in the oilseed Brassica juncea: importance of recurrent selection backcross scheme for the identification of 'true' QTL

Seed glucosinolate content in Brassica juncea is a complex quantitative trait. A recurrent selection backcross (RSB) method with a doubled haploid (DH) generation interspersing backcross generations was used for the introgression of low glucosinolate alleles from an east European gene pool B. juncea line, Heera into an Indian gene pool variety, Varuna. Phenotypic comparisons among the DH populations derived from early to advanced backcrosses revealed a shift in the mean values for various glucosinolates with the advancement of backcrossing, indicating a change in the selective values of the alleles with change in the genetic background due to the existence of epistasis and context dependencies. QTL mapping for various seed glucosinolates from early (F(1)DH) and advanced generation (BC(4)DH) populations confirmed the presence of epistasis and context dependency. The common QTL detected in both F(1)DH and BC(4)DH changed their R (2) values from the former to the later generation. Some of the QTL detected in the F(1)DH became irrelevant in the BC(4)DH population. Further, new QTL were detected in the BC(4)DH population for various glucosinolates. A validation study on a population of low glucosinolate DH lines derived from all the backcross generations of the RSB breeding programme revealed that the QTL detected in BC(4)DH were the 'true' QTL. Using glucosinolate as an example, the study provides strong evidence for the importance of the RSB method for the identification of the 'true' QTL which would be significant for marker assisted introgression of a complex quantitative trait whose expression is influenced by epistatic interactions.

Mapping of yield influencing QTL in Brassica juncea: implications for breeding of a major oilseed crop of dryland areas

Quantitative trait loci (QTL) analysis of yield influencing traits was carried out in Brassica juncea (AABB) using a doubled haploid (DH) mapping population of 123 lines derived from a cross between Varuna (a line representing the Indian gene pool) and Heera (representing the east European gene pool) to identify potentially useful alleles from both the parents. The existing AFLP based map of B. juncea was further saturated with RFLP and SSR markers which led to the identification of the linkage groups belonging to the A (B. rapa) and B (B. nigra) genome components of B. juncea. For QTL dissection, the DH lines were evaluated at three different environments and phenotyped for 12 quantitative traits. A total of 65 QTL spread over 13 linkage groups (LG) were identified from the three environments. QTL analysis showed that the A genome has contributed more than the B genome to productivity (68% of the total QTL detected) suggesting a more prominent role of the A genome towards domestication of this crop. The east European line, Heera, carried favorable alleles for 42% of the detected QTL and the remaining 58% were in the Indian gene pool line, Varuna. We observed clustering of major QTL in a few linkage groups, particularly in J7 and J10 of the A genome, with QTL of different traits having agronomically antagonistic allelic effects co-mapping to the same genetic interval. QTL analysis also identified some well-separated QTL which could be readily transferred between the two pools. Based on the QTL analysis, we propose that improvement in yield could be achieved more readily by heterosis breeding rather than by pure line breeding.

A new cytoplasmic male sterility system for hybrid seed production in Indian oilseed mustard Brassica juncea

We report a novel cytoplasmic male sterility (CMS) system in Brassica juncea (oilseed mustard) which could be used for production of hybrid seed in the crop. A male sterile plant identified in a microspore derived doubled haploid population of re-synthesized B. napus line ISN 706 was found to be a CMS as the trait was inherited from the female parent. This CMS, designated '126-1', was subsequently transferred to ten different B. juncea varieties and lines through inter-specific crosses followed by recurrent backcrossing. The F(1)s of inter-specific crosses were invariably partially fertile, but irrespective of the variety/line used, the recipient lines became progressively male sterile over five to seven generations and could be maintained by crossing the male sterile lines with their normal counterparts. The male sterile lines were found to be stable for the trait under both long and short day conditions. CMS lines when crossed with lines other than the respective maintainer line were restored for fertility, implying that any variety could act as a restorer for '126-1' cytoplasm in B. juncea. These unique features in maintenance and restoration of CMS lines coupled with near normal floral morphology of the CMS lines have allowed the use of '126-1' cytoplasm for hybrid seed production. The uniqueness of '126-1' has been further established by Southern hybridization with mitochondrial DNA probes and by a histological study of the development of male sterile anthers.

Mapping and tagging of seed coat colour and the identification of microsatellite markers for marker-assisted manipulation of the trait in Brassica juncea

Microsatellite marker technology in combination with three doubled haploid mapping populations of Brassica juncea were used to map and tag two independent loci controlling seed coat colour in B. juncea. One of the populations, derived from a cross between a brown-seeded Indian cultivar, Varuna, and a Canadian yellow-seeded line, Heera, segregated for two genes coding for seed coat colour; the other two populations segregated for one gene each. Microsatellite markers were obtained from related Brassica species. Three microsatellite markers (Ra2-A11, Na10-A08 and Ni4-F11) showing strong association with seed coat colour were identified through bulk segregant analysis. Subsequent mapping placed Ra2-A11 and Na10-A08 on linkage group (LG) 1 at an interval of 0.6 cM from each other and marker Ni4-F11 on LG 2 of the linkage map of B. juncea published previously (Pradhan et al., Theor Appl Genet 106:607-614, 2003). The two seed coat colour genes were placed with markers Ra2-A11 and Na10-A08 on LG 1 and Ni4-F11 on LG 2 based on marker genotyping data derived from the two mapping populations segregating for one gene each. One of the genes (BjSC1) co-segregated with marker Na10-A08 in LG 1 and the other gene (BjSC2) with Ni4-F11 in LG 2, without any recombination in the respective mapping populations of 130 and 103 segregating plants. The identified microsatellite markers were studied for their length polymorphism in a number of yellow-seeded eastern European and brown-seeded Indian germplasm of B. juncea and were found to be useful for the diversification of yellow seed coat colour from a variety of sources into Indian germplasm.

Plant codon optimized cry genes of Bacillus thuringiensis can be expressed as soluble proteins in Escherichia coli BL21 Codon Plus strain as NusA-Cry protein fusions

For optimal expression of delta-endotoxins from Bacillus thuringiensis in plants, preferential changes in the codon sequences, and reduction in overall AT content in the nucleotide sequence of the genes is important. Reports suggest that sequences with such modifications cannot be overexpressed in bacteria. We report here that the modified genes can be overexpressed in a strain of Escherichia coli carrying extra tRNA genes for some of the codons occurring at high frequency in plant genes and less preferred in E. coli. We also demonstrate that proteins when expressed as fusion products with NusA protein, are obtained as soluble fraction rather than in inclusion bodies. This allows easy and accurate LC50 analysis on insect pests.

Molecular tagging of erucic acid trait in oilseed mustard (Brassica juncea) by QTL mapping and single nucleotide polymorphisms in FAE1 gene

Molecular mapping and tagging of the erucic acid trait (C22:1) in Brassica juncea was done by a candidate gene approach. Two QTLs underlying the variation of seed erucic acid content were assigned to two linkage groups of a B. juncea map using a doubled haploid (DH) mapping population derived from high x low erucic acid F(1) hybrid. Two consensus primers corresponding to the full-length Fatty Acid Elongase 1 ( FAE1) gene, reported to be involved in the elongation of C18:1 to C22:1, were designed. PCR amplification and subsequent cloning and sequencing identified two FAE1 genes ( FAE1.1 and FAE1.2) in both high and low erucic acid mustard lines. Sequence alignment of corresponding FAE1 genes between high and low erucic acid mustard lines identified four substitution type single nucleotide polymorphisms (SNPs) in FAE1.1 and three in FAE1.2. Using the SNuPE method of SNP genotyping, these two genes were mapped to two independent loci that co-segregated with the two QTLs governing the erucic acid trait. Association of wild ( E1E2) and mutant ( e1e2) haplotypes of two FAE1 genes with erucic acid variation in two segregating populations revealed that the e1e1e2e2 genotype identified low erucic acid individuals (<2%) and E1E1E2E2 identified individuals with highest erucic acid content (>40%). The E1e1E2e2 heterozygote was found to be intermediate in phenotype. The applicability of these SNPs in marker-assisted manipulation of the erucic acid trait was verified by genotyping a set of contrasting germplasm of B. juncea belonging to two distinct gene pools (Indian and east European) and other oil-yielding Brassica species.

Slow desiccation leads to high-frequency shoot recovery from transformed somatic embryos of cotton (Gossypium hirsutum L. cv. Coker 310 FR)

In Agrobacterium-mediated genetic transformation of cotton (Gossypium hirsutum L. cv. Coker 310FR) the frequency at which somatic embryos were converted to plantlets was significantly improved by subjecting the embryos to slow physical desiccation. We used Agrobacterium strain GV3101 containing the binary vector pGSFR with the nos-nptII gene for in vitro selection and the 35S gus-int fragment as a reporter to optimize the transformation protocol. Although the concentration of kanamycin was reduced during embryogenesis and embryo maturation, even at the lower levels somatic embryos were predominantly abnormal, showing hypertrophy and reduced or fused cotyledons or poor radicle ends. A majority of these embryos (more than 75%) were beta-glucuronidase (GUS)-positive. Embryos with an abnormal appearance showed a very poor conversion to plantlets. However, these embryos, when subjected to slow physical desiccation followed by transfer to fresh medium, regenerated single or multiple shoots from the cotyledonary end. These shoots could be grafted on wild-type seedling stocks in vitro, which, following their transfer to soil, developed normally and set seeds. Regenerated plants tested positive for the transgene by Southern analysis. An overall scheme for the high-frequency production of cotton transgenics from both normal and abnormal appearing somatic embryos is presented.

A high-density linkage map in Brassica juncea (Indian mustard) using AFLP and RFLP markers

A high-density genetic linkage map of Brassica juncea (2n = 36) was constructed with 996 AFLP (amplified fragment length polymorphism) and 33 RFLP (restriction fragment length polymorphism) markers using a F1-derived doubled-haploid (DH) population of 123 individuals. This mapping population was developed by crossing a well-adapted, extensively grown Indian variety Varuna and a canola quality line Heera. The two lines are highly divergent and contain a number of contrasting qualitative and quantitative traits of high agronomic value. AFLPs were generated by the use of restriction enzymes EcoRI or PstI in combination with either MseI or TaqI. Using 91 primer pairs, a total of 1,576 parental polymorphic bands were detected of which 996 were used for mapping. In addition, 33 RFLP markers, developed from genomic clones of B. napus, were added to the map. The segregation of each marker and linkage analysis was performed using the program JoinMap version 2.0. The 1,029 mapped-markers were aligned in 18 linkage groups, which is the haploid chromosome number of the species, at LOD values ranging from 5 to 8. The total map length was 1,629 cM with an average marker interval of 3.5 cM. AFLP markers generated by EcoRI were more clustered, whereas PstI markers showed more extensive distribution. A set of 26 primer pairs (9 EcoRI/ MseI, 6 EcoRI/ TaqI, 6 PstI/ MseI and 5 PstI/ TaqI) generating 385 markers were identified for AFLP-based whole-genome selection as these markers covered 96% of the genome mapped with the 91 primer pairs. The map developed in the present study could be used for dissection and the transfer of agronomically important traits and favourable QTLs from ill-adapted exotic germplasm to cultivated Indian varieties.

A four-element based transposon system for allele specific tagging in plants--theoretical considerations

The two-element transposon constructs, utilizing either Ac/Ds or Spm/dSpm, allow random tagging of genes in heterologous model species, but are inadequate for directed tagging of specific alleles of agronomic importance. We propose the use of Ac/Ds in conjunction with Spm/dSpm to develop a four-element system for directed tagging of crop-specific alleles. The four-element based construct would include both Ds and dSpm along with relevant marker genes and would function in two steps. In the first step dSpm(Ds) stocks (a minimum of two) would be crossed to a line containing transposases of Spm and unlinked integrations would be selected from segregating population by the use of a negative selection marker to develop stocks representing integration of dSpm(Ds) at a large number of locations in the genome. Selections would be made for a line in which dSpm(Ds) shows partial or complete linkage to the allele of interest. In the second step selected line would be crossed to a line containing Ac transposase to induce transpositions of Ds element to linked sites thereby exploiting the natural tendency of Ds element to jump to linked sites. Unlinked jumps of dSpm(Ds) and linked jumps of Ds could be monitored by appropriate marker genes. The proposed model would allow tagging of allele of interest in chromosome addition lines and also help in the efficient use of genic male sterility systems for hybrid seed production by tightly marking the fertility restorer gene with a negative selection marker.

Synthesis of hexaploid (AABBCC) somatic hybrids: a bridging material for transfer of 'tour' cytoplasmic male sterility to different Brassica species

Most of the alloplasmic cytoplasmic male sterility (CMS) systems are known to be associated with a number of floral abnormalities that result from nuclear-cytoplasmic incompatibilities. One such system, 'tour', which is derived from Brassica tournefortii, induces additional floral abnormalities and causes chlorosis in Brassica spp. While the restorer for this CMS has been reported to be present in B. napus, in B. juncea, where the abnormalities are more pronounced, no restorer has yet been identified. Rectification of these floral abnormalities through mitochondrial recombinations and chloroplast replacement might result in the improvement of this CMS system. As organelle recombinations can possibly be achieved only by somatic cell hybridization, fusion experiments were carried out between hygromycin-resistant B. juncea AABB carrying 'tour' cytoplasm and phosphinotricin-resistant, normal B. oleracea CC to generate AABBCC hexaploid somatic hybrids. The presence of selectable marker genes facilitated the selection of hybrids in large numbers. The resulting hybrids showed wide variation in floral morphology and organelle composition. Regenerants with normal, male-sterile flowers having recombinant 'tour'-or 'oleracea'-type mitochondria and 'oleracea'-type chloroplasts were obtained. Hybrids with male-fertile flowers were also obtained that had recombined 'tour' mitochondria. The AABBCC hexaploid hybrids synthesized in the present study were successfully utilized as a bridging material for transferring variability in the organelle genome simultaneously to all the digenomic Brassica species, and all of these hybrids are now being stabilized through repeated backcrosses to the allopolyploid crop brassicas.

Transfer of Brassica tournefartii (TT) genes to allotetraploid oilseed Brassica species (B. juncea AABB, B. napus AACC, B. carinata BBCC): homoeologous pairing is more pronounced in the three-genome hybrids (TACC, TBAA, TCAA, TCBB) as compared to allodiploids (TA, TB, TC)

For the transfer of genes from B. tournefortii (TT) to the allotetraploid oilseed brassicas, B. juncea AABB, B. carinata BBCC and B. napus AACC, B. tournefortii was first crossed with the three basic diploid species, B. campestris (AA), B. nigra (BE) and B. oleracea (CC), to produce the allodiploids TA, TB and TC. These were tetraploidized by colchicine treatment to produce the allotetraploids TTAA, TTBB and TTCC, which were further crossed with B. juncea and B. napus to produce three-genome hybrids with substitution-type genomic configurations: TACC, TBAA and TCAA. These hybrids along with another hybrid TCBB produced earlier, the three allodiploids, their allotetraploids and the four diploid parent species were studied for their male meiotic behaviour. The diploid parent and the allotetraploids (TTAA, TTBB and TTCC) showed regular meiosis although the pollen viability was generally low in the allotetraploids. In the allodiploids (TA, TB and TC) only some end-to-end associations were observed without any clearly discernible chiasmata or exchange points. Chromosomes involved in end-to-end associations were randomly distributed at the metaphase/anaphase-I stages. In contrast, the three-genome hybrids (TACC, TBAA, TCAA and TCBB) showed normal bivalents whose number exceeded the expected bivalent values. Bivalents arising out of homoeologous pairing were indistinguishable from normal pairs by their disjunction pattern but could be distinguished on the basis of the heteromorphy of the homoeologous chromosomes. The three-genome hybrids could be backcrossed to allotetraploid oilseed brassicas as they had some fertility. In contrast, the allodiploids could neither be selfed nor back-crossed. On the basis of their meiotic stability, in terms of more pronounced homoeologous pairing and fertility for backcrossing, the three-genome configurations provide the best possible situation for the introgression of alien genes from the secondary gene pool to the allotetraploid oilseed crops B. juncea, B. napus and B. carinata.

Somatic hybrids with substitution type genomic configuration TCBB for the transfer of nuclear and organelle genes from Brassica tournefortii TT to allotetraploid oilseed crop B. carinata BBCC

Oilseed crop Brassica carinata BBCC is a natural allotetraploid of diploid species B. nigra BB and B. oleracea CC. To transfer the nuclear and organelle genes in a concerted manner from an alien species, B. tournefortii TT, to B. carinata, we produced somatic hybrids with genomic configuration TCBB using B. nigra and B. oleracea stocks that carried selectable marker genes. B. tournefortii TT was sexually crossed with hygromycin-resistant B. oleracea CC. Protoplasts isolated from shoot cultures of hygromycin-resistant F1 hybrids of B. tournefortiixB. oleracea TC were fused with protoplasts of kanamycin-resistant B. nigra BB. In two different fusion experiments 80 colonies were obtained through selection on media containing both hygromycin and kanamycin. Of these, 39 colonies regenerated into plants. Analysis of 15 regenerants by random amplified polymorphic DNA (RAPD) markers showed the presence of all three genomes, thereby confirming these to be true hybrids. Restriction fragment length polymorphism (RFLP) analysis of organelle genomes with heterologous chloroplast (cp)and mitochondrial (mt) DNA probes showed that the chloroplast genome was inherited from either of the two parents while mitochondrial genomes predominantly showed novel configurations due to either rearrangements or intergenomic recombinations. We anticipate that the TCBB genomic configuration will provide a more conducive situation for recombination between the T and C genomes during meiosis than the TTCCBB or TCCBB type configurations that are usually produced for alien gene transfer. The agronomic aim of producing TCBB hybrids is to transfer mitochondrial genes conferring cytoplasmic male sterility and nuclear genes for fertility restoration from B. tournefortii to B. carinata.

Regeneration of pigeonpea (Cajanus cajan) from cotyledonary node via multiple shoot formation

Plant regeneration, which is the major limiting factor for transformation of Cajanus cajan, has been obtained via multiple shoot formation from the cotyledonary node region of seedlings germinated on MS medium containing 2 mgl(-1) 6-benzylaminopurine. A mass of multiple shoot-initials formed at the axillary bud region of the cotyledonary node of the seedlings within two weeks. The cotyledonary node along with the mass of shoot-initials excised from the seedling, continued to form new shoot-initials on MS medium containing 6-benzylaminopurine (2 mgl(-1)) and supplemented topically with indole-3-acetic acid. The formation of new shoot-initials was also observed from the cotyledonary nodal explant, after cutting off its surface layers to completely remove the pre-existing shoot-initials and culturing it on 6-benzylaminopurine (2 mgl(-1)) containing medium. The shoots elongated rapidly on basal MS medium and rooted efficiently in MS medium supplemented with indole-3-butyric acid (0.5 mgl(-1)). The procedure described is efficient, and highly reproducible and a common response was observed for all the six varieties tested.

Variation amongst Brassica juncea cultivars for regeneration from hypocotyl explants and optimization of conditions for Agrobacterium-mediated genetic transformation

Twelve cultivars of Brassica juncea grown in different agroclimatic regions of the world were tested for their ability to regenerate in vitro from hypocotyl explants and, accordingly, were divided into three groups. One group of cultivars regenerated on MS medium supplemented with 2,4-D, BAP and with NAA, BAP combinations; another group regenerated only on MS with 2,4-D, BAP; and the third group showed very low regeneration on both of these combinations. Inclusion of silver nitrate in the medium was essential for high frequency of regeneration. In general, Indian cultivars were more responsive than the cultivars of CIS and Australian origin. Using the media optimal for regeneration and an Agrobacterium-based binary vector carrying hpt and gus-intron genes, conditions for genetic transformation of B. juncea hypocotyl explants were optimized. Transformation frequencies, identified by GUS staining at the initial stages of growth, were lower on MS medium with 2,4-D, BAP than on MS with NAA, BAP. Plants resistant to 20 μg/ml hygromycin were regenerated at a frequency of 11-36% from hypocotyl explants and were shown to be transformed by Southern blotting, GUS staining and progeny analysis.

Phytogeny of Brassica and allied genera based on variation in chloroplast and mitochondrial DNA patterns: molecular and taxonomic classifications are incongruous

Chloroplast DNA (cpDNA) variability of 60 taxa of the genus Brassica and allied genera comprising 50 species was studied. RFLPs for seven enzymes were generated and F values were estimated from five frequently cutting enzymes. Phenetic clusterings indicated a clear division of Brassica coenospecies into two distinct lineages referred to as the Brassica and Sinapis lineages. Two unexplored genera, Diplotaxis and Erucastrum, also exhibited two lineages in addition to the genera Brassica and Sinapis. This finding is inconsistent with the existing taxonomic classification based on morphology. Mitochondrial DNA (mtDNA) variability studied from EcoRI RFLP patterns, by hybridizing total DNA with four cosmid clones containing non-overlapping mtDNA fragments, did not show any congruence with cpDNA variation patterns. However, at the cytodeme level, the patterns of genetic divergence suggested by the cpDNA data could be correlated with mtDNA variation. In the Brassica lineage, Diplotaxis viminea was identified as the female parent of the allotetraploid D. muralis. The chloroplast DNAs of Erucastrum strigosum and Er. abyssinicum were found to be very closely related. In the Sinapis lineage, Brassica maurorum was found to be the diploid progenitor of autotetraploid B. cossoneana. B. amplexicaulis showed a very different cpDNA pattern from other members of the subtribe. Brassica adpressa was closest to Erucastrum laevigatum and could be the diploid progenitor of autotetraploid Er. laevigatum. Based on the close similarity of the cpDNA pattern of Diplotaxis siifolia with that of D. assurgens, we have proposed the retention of this species in the genus Diplotaxis. The taxonomic positions of some other species have also been discussed.

Agrobacterium-mediated genetic transformation of oilseed Brassica campestris: Transformation frequency is strongly influenced by the mode of shoot regeneration

Protocols were developed for efficient shoot regeneration from hypocotyl and cotyledon explants of oilseed Brassica campestris (brown sarson) cv. 'Pusa Kalyani'. These were used for genetic transformation by an Agrobacterium based binary vector carrying neomycin phosphotransferase (npt) gene and β-glucuronidase (gus)-intron gene for plant cell specific expression. Transformed plants were recovered from hypocotyl explants at a frequency of 7-13%. Addition of silver nitrate markedly enhanced shoot regeneration in hypocotyl explants under non-selection conditions and was found to be an absolute requirement under selection conditions. Cotyledon explants, inspite of being more regenerative, proved to be highly refractory to transformation. Only two chimeric transformed shoots were obtained from more than 10,000 cotyledons treated with Agrobacterium. In hypocotyl explants, shoot regeneration occurred from the vascular parenchyma both with and without the intervention of callus phase. Only the shoot buds differentiating from callus tissue were positive for GUS activity. In cotyledons, shoot buds originated only directly from the vascular parenchyma, generally at a distance of about 450-625 μ from the cut surface. Such shoots were negative for GUS activity.

Mitochondrial DNA patterns are similar in gametosomatic and somatic hybrids of two Nicotiana species

The segregation and recombination patterns of mitochondrial genome in the somatic hybrids of Nicotiana tabacum and N. rustica were studied by RFLP analysis using four heterologous mitochondrial DNA probes, namely cytochrome oxidase subunit I (COI), cytochrome oxidase subunit II (COII), 26s rDNA and 5s-18s rDNA. These RFLP patterns were compared with those of the gametosomatic hybrids of these two species. A preponderance of N. rustica type patterns was observed in the somatic hybrids. One of the somatic hybrids had N. rustica type pattern with COI probe, novel pattern with COII, and 26s rDNA probe and N. tabacum type pattern with 5s-18s rDNA probe. These patterns are identical to those of some of the gametosomatic hybrids and could only be due to the recombination of mitochondrial genomes of the two parents. The extent and the nature of recombination of mitochondrial genomes is similar in gametosomatic and somatic hybrids.

Efficient regeneration of Brassica oleracea hypocotyl protoplasts and high frequency genetic transformation by direct DNA uptake

Efficient regeneration (80%) and high frequency genetic transformation (10-33%) were achieved by culturing protoplasts isolated from hypocotyl tissues of six day old Brassica oleracea seedlings and by subjecting these protoplasts to PEG mediated direct plasmid uptake. Three different plasmid vectors carrying marker genes for resistance to methotrexate (dhfr), hygromycin (hpt) and phosphinotricin (bar) were constructed and used for transformation. Large number of normal, fertile transformants were obtained with vectors carrying hpt and bar genes. No transformants could be regenerated for resistance to methotrexate as it severely suppressed shoot differentiation.

Transmission of organelles in triploid hybrids produced by gametosomatic fusions of two Nicotiana species

Gametosomatic hybrids produced by the fusion of microspore protoplasts of Nicotiana tabacum Km(+)Sr(+) with somatic cell protoplasts of N. rustica were analysed for their organelle composition. For the analysis of mitochondrial (mt)DNA, species-specific patterns were generated by Southern hybridization of restriction endonuclease digests of total DNA and mtDNA with four DNA probes of mitochondrial origin: cytochrome oxidase subunit I, cytochrome oxidase subunit II, 26s rDNA and 5s-18s rDNA. Of the 22 hybrids analyzed, some had parental-type pattern for some probes and novel-type for the others, indicating interaction between mtDNA of the two parent species. For chloroplast (cp)DNA analysis, species-specific patterns were generated by Southern hybridization of restriction endonuclease digests of total DNA with large subunits of ribulose bisphosphate carboxylase and cpDNA as probes. All the hybrids had N. rustica-specific patterns. Hybrids were not resistant to streptomycin, a trait encoded by the chloroplast genome of N. tabacum. In gametosomatic fusions of the two Nicotiana species, mitochondria but not the chloroplasts are transmitted from the parent contributing microspore protoplasts.

A selection method for the synthesis of triploid hybrids by fusion of microspore protoplasts (n) with somatic cell protoplasts (2n)

Microspore protoplasts (n) isolated at the tetrad stage from plants of Nicotiana tabacum Km(+) (2n=4x=48) were fused with somatic cell protoplasts (2n) of WT N. rustica (2n=4x=48) to produce triploid plants. A total of 21.2×10(6) microspore protoplasts were fused with 11.2×10(6) somatic cell protoplasts using the high pH/Ca(+ +) method. Microspore protoplasts did not divide and WT N. rustica protoplasts stopped dividing when the protoplast-derived colonies were transferred to a selection medium containing kanamycin. A total of 104 actively growing green colonies were recovered on the selection medium. Ninety-six of these colonies were tested for their hybrid nature by PAGE of peroxidases and were found to contain bands characteristic of both parents. Hybrid nature of the plants regenerated from some of the selected colonies was confirmed by IEF of leaf esterases, by NPT II activity assay and by hybridizing total DNAs restricted with EcoR I to a cloned 18s rDNA fragment. Root tip squashes of six of the hybrid plants revealed chromosome numbers ranging from 58-72. From chromosomal and biochemical analysis, it can be concluded that the procedure of fusing microspore protoplasts (n) of species A carrying a dominant selection marker with WT somatic cell protoplasts (2n) of species B can be a convenient selection method for the synthesis of triploid plants. The significance of triploids lies in their subsequent use for transferring alien chromosomes and genes of species A to species B.

Analysis of fertility in somatic hybrids of Nicotiana rustica and N. tabacum and progeny over two sexual generations

Somatic hybrid plants, produced between Nicotiana rustica and N. tabacum by heterokaryon isolation and culture and also by mutant complementation, were examined regarding their ability to set seed. From a total of seventeen independent somatic hybrids, three were found to be partially self-fertile while the others did not set seed. Differences regarding the methods of hybrid selection, parental varieties and chloroplast composition of hybrids did not appear to be significant regarding the ability of plants to set seed. Much variation in fertility was observed in subsequent generations and by recurrent selection of the most fertile, over two generations, it was possible to increase the level of self-fertility in some of the progeny. One R2 derivative possessed approximately a tenfold higher level of self-fertility than it's somatic hybrid parent. The presence of genetic markers from both parents were observed in all progeny indicating their hybrid nature.

Interrelationship of cultivated rices Oryza sativa and O. glaberrima with wild O. perennis complex : Analysis of fraction 1 protein and some repeated DNA sequences

Phylogenetic relationship of the cultivated rices Oryza sativa and O. glaberrima with the O. perennis complex, distributed on the three continents of Asia, Africa and America, and O. australiensis has been studied using Fraction 1 protein and two repeated DNA sequences as markers. Fraction 1 protein isolated from the leaf tissue of accessions of different species was subjected to isoelectric focusing. All the species studied have similar nuclear-encoded small subunit polypeptides and chloroplast-encoded large subunit polypeptides, except two of the O. perennis accessions from South America and O. australiensis, which have a different pattern for the chloroplast subunit. Two DNA sequences were isolated from Eco R1 restriction endonuclease digests of total DNA from O. sativa. One of the sequences has been characterized as highly repeated satellite DNA, and the other one as a moderately repeated DNA sequence. These sequences were used as probes in DNA/DNA hybridization with restriction endonuclease digested DNA from some accessions of the different species. Those accessions that are divergent for large subunit polypeptides of Fraction 1 protein (O. australiensis and two of the four South American O. perennis accessions) also lack the satellite DNA and have a different hybridization pattern with the moderately repeated sequence. All other accessions, irrespective of their geographical origin, are similar. We propose that various accessions of O. perennis from Africa and Asia are closely related to O. sativa and O. glaberrima, and that the dispersal of cultivated and O. perennis rices to different continents may be quite recent. The American O. perennis is a heterogeneous group. Some of the accessions ascribed to this group are closely related to the Asian and African O. perennis, while others have diverged.