Comparative proteomics reveals differential induction of both biotic and abiotic stress response associated proteins in rice during Xanthomonas oryzae pv. oryzae infection

Xanthomonas oryzae pv. oryzae (Xoo) causes bacterial blight disease in rice and brutally affects the yield up to 50 % of total production. Here, we report a comparative proteomics analysis of total foliar protein isolated from infected rice leaves of susceptible Pusa Basmati 1 (PB1) and resistant Oryza longistaminata genotypes. Two-dimensional gel electrophoresis (2-DE) coupled with matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) approaches identified 29 protein spots encoding unique proteins from both the genotypes. Identified proteins belonged to a large number of biological and molecular functions related to biotic and abiotic stress proteins which are potentially involved during Xoo infection. Biotic and abiotic stress-related proteins were induced during Xoo infection, indicating the activation of common stress pathway during bacterial blight infection. Candidate genes conferring tolerance against bacterial blight, which include germin-like protein, putative r40c1, cyclin-dependent kinase C, Ent-isokaur-15-ene synthase and glutathione-dependent dehydroascorbate reductase 1 (GSH-DHAR1), were also induced, with germin-like proteins induced only in the resistant rice genotype O. longistaminata. Energy, metabolism and hypothetical proteins were common among both the genotypes. Further, host defence/stress-related proteins were mostly expressed in resistant genotype O. longistaminata, indicating possible co-evolution of the pathogen and the wild rice, O. longistaminata.

Characterization of a pathogen induced thaumatin-like protein gene AdTLP from Arachis diogoi, a wild peanut

Peanut (Arachis hypogaea L) is one of the widely cultivated and leading oilseed crops of the world and its yields are greatly affected by various biotic and abiotic stresses. Arachis diogoi, a wild relative of peanut, is an important source of genes for resistance against various stresses that affect peanut. In our previous study a thaumatin-like protein gene was found to be upregulated in a differential expression reverse transcription PCR (DDRT-PCR) study using the conidial spray of the late leaf spot pathogen, Phaeoisariopsis personata. In the present study, the corresponding full length cDNA was cloned using RACE-PCR and has been designated as AdTLP. It carried an open reading frame of 726 bp potentially capable of encoding a polypeptide of 241 amino acids with 16 conserved cysteine residues. The semi-quantitative RT-PCR analysis showed that the transcript level of AdTLP increased upon treatment with the late leaf spot pathogen of peanut, P. personata and various hormone treatments indicating its involvement in both, biotic and abiotic stresses. The antifungal activity of the purified recombinant protein was checked against different fungal pathogens, which showed enhanced anti-fungal activity compared to many other reported TLP proteins. The recombinant AdTLP-GFP fusion protein was found to be predominantly localized to extracellular spaces. Transgenic tobacco plants ectopically expressing AdTLP showed enhanced resistance to fungal pathogen, Rhizoctonia solani. The seedling assays showed enhanced tolerance of AdTLP transgenic plants against salt and oxidative stress. The transcript analysis of various defense related genes highlighted constitutively higher level expression of PR1a, PI-I and PI-II genes in transgenic plants. These results suggest that the AdTLP is a good candidate gene for enhancing stress resistance in crop plants.

Novel role for a serine/arginine-rich splicing factor, AdRSZ21 in plant defense and HR-like cell death

A splicing factor gene belonging to the serine/arginine (SR)-rich protein family was cloned from Arachis diogoi, a wild relative of peanut in a study on differential gene expression and was designated as AdRSZ21. AdRSZ21 exhibits a RNA recognition motif (RRM), a CCHC type zinc finger domain (Zinc Knuckle, ZnK) and a C-terminal RS domain that is rich in arginine and serine. Multiple sequence alignment of AdRSZ21 with putative orthologs from diverse taxa including lower plants and monocots showed that the RRM and ZnK domains are evolutionarily conserved. Phylogenetic studies revealed that AdRSZ21 belongs to the RSZ subfamily and is closely related to the Arabidopsis ortholog AtRSZ22. Transient constitutive and conditional heterologous expression of AdRSZ21 resulted in HR-like cell death in tobacco leaves. The presence of a functional RRM domain, but not ZnK domain was essential for AdRSZ21 induced HR-like cell death phenotype. On the other hand, expression of AdRSZ21 with mutated ZnK domain lead to accelerated cell death. The cell death induced by AdRSZ21 was found to be associated with specific upregulation of patatin-like protein gene and other defense related gene transcripts suggesting a role for AdRSZ21 in plant defense and HR-like cell death.

Expression of chitinase genes of Metarhizium anisopliae isolates in lepidopteran pests and on synthetic media

Pathogenecity of the well characterized entomopathogenic fungus Metarhizium anisopliae used for biocontrol of a wide range of insect pests secretes hydrolytic enzymes that degrade the host cuticle. The chitinolytic activity of high and low virulent isolates of M. anisopliae was assayed on minimal medium (MM) + colloidal chitin and MM supplemented with insect cuticles. Ex- pression pattern of four chitinase genes (chitinase (chi), chi 1, chi 2, chi 3) was profiled during pathogenic stages of the entomopathogen under in vitro and in vivo conditions. Reverse-transcription polymerase chain reaction (RT-PCR) analysis confirmed that chitinase cDNAs were expressed during the germination of fungus under nutrient-deprived conditions. RT-PCR analysis performed for the four chitinase genes on the two insect hosts Spodoptera litura and Helicoverpa armigera at six developmental stages of the pathogen displayed up-regulation in S. litura at mycosed and conidiated condition while with H. armigera there was expression only after 48 h of incubation. Differential expression of chi, chi 1 and chi 2 genes in vitro (nitrogen rich and nitrogen limiting media) and in vivo (live insect hosts S. litura and H. armigera) implicate the role of substrate differences in pathogenesis.

Identification and characterization of annexin gene family in rice

Plant annexins are Ca(2+)-dependent phospholipid-binding proteins and are encoded by multigene families. They are implicated in the regulation of plant development as well as protection from drought and other stresses. They are well characterized in Arabidopsis, however no such characterization of rice annexin gene family has been reported thus far. With the availability of the rice genome sequence information, we have identified ten members of the rice annexin gene family. At the protein level, they share 16-64% identity with predicted molecular masses ranging from 32 to 40 kDa. Phylogenetic analysis of rice annexins together with annexins from other monocots led to their classification into five different orthologous groups and share similar motif patterns in their protein sequences. Expression analysis by real-time RT-PCR revealed differential temporal and spatial regulation of these genes. The rice annexin genes are also found to be regulated in seedling stage by various abiotic stressors including salinity, drought, heat and cold. Additionally, in silico analysis of the putative upstream sequences was analyzed for the presence of stress-responsive cis-elements. These results provide a basis for further functional characterization of specific rice annexin genes at the tissue/developmental level and in response to abiotic stresses.

Enhanced antifungal and insect α-amylase inhibitory activities of Alpha-TvD1, a peptide variant of Tephrosia villosa defensin (TvD1) generated through in vitro mutagenesis

TvD1 is a small, cationic, and highly stable defensin from the weedy legume, Tephrosia villosa with demonstrated in vitro antifungal activity. We show here peptide modifications in TvD1 that lead to enhanced antifungal activities. Three peptide variants, S32R, D37R, and Alpha-TvD1 (-G-M-T-R-T-) with variations in and around the β2-β3 loop region that imposes the two β-strands, β2 and β3 were generated through in vitro mutagenesis. Alpha-TvD1 exhibited enhanced antifungal activity against the fungal pathogens, Fusarium culmorum and Fusarium oxysporum with respective IC(50) values of 2.5 μM and 3.0 μM, when compared to S32R (<5.0 μM and >5.0 μM), D37R (5.5 μM and 4.5 μM), and the wild type TvD1 (6.5 μM). Because of the enhanced antifungal activity, this variant peptide was characterized further. Growth of F. culmorum in the presence of Alpha-TvD1 showed deformities in hyphal walls and nuclear damage. With respect to the plant pathogenic bacterium, Pseudomonas syringae pv. tomato strain DC3000, both Alpha-TvD1 and the wild type TvD1 showed comparable antibacterial activity. Both wild type TvD1 and Alpha-TvD1 displayed inhibitory activity against the α-amylase of the mealworm beetle, Tenebrio molitor (TMA) with the latter showing enhanced activity. The human salivary as well as barley α-amylase activities were not inhibited even at concentrations of up to 50 μM, which has been predicted to be due to differences in the pocket size and the size of the interacting loops. Present study shows that the variant Alpha-TvD1 exhibits enhanced antifungal as well as insect α-amylase inhibitory activity.

Mungbean plants expressing BjNPR1 exhibit enhanced resistance against the seedling rot pathogen, Rhizoctonia solani

Mungbean, Vigna radiata (L.) Wilczek is an important pulse crop that is widely cultivated in semi- arid tropics. The crop is attacked by various soil-borne pathogens like Rhizoctonia solani, which causes dry rot disease and seriously affects its productivity. Earlier we characterized the non-expressor of pathogenesis related gene-1(BjNPR1) of mustard, Brassica juncea, the counterpart of AtNPR1 of Arabidopsis thaliana. Here, we transformed mungbean with BjNPR1 via Agrobacterium tumefaciens. Because of the recalcitrant nature of mungbean, the effect of some factors like Agrobacterium tumefaciens strains (GV2260 and LBA4404), pH, L: -cysteine and tobacco leaf extract was tested in transformation. The transgenic status of 15 plants was confirmed by PCR using primers for nptII. The independent integration of T-DNA in transgenic plants was analyzed by Southern hybridization with an nptII probe and the expression of BjNPR1 was confirmed by RT-PCR. Some of the T(0) plants were selected for detached leaf anti-fungal bioassay using the fungus Rhizoctonia solani, which showed moderate to high level of resistance depending on the level of expression of BjNPR1. The seedling bioassay of transgenic T(2) plants indicated resistance against dry rot disease caused by R. solani.

Constitutive expression of mustard annexin, AnnBj1 enhances abiotic stress tolerance and fiber quality in cotton under stress

Annexins belong to a multigene family of Ca(2+) dependent, phospholipid and cytoskeleton binding proteins. They have been shown to be upregulated under various stress conditions. We generated transgenic cotton plants expressing mustard annexin (AnnBj1), which showed enhanced tolerance towards different abiotic stress treatments like sodium chloride, mannitol, polyethylene glycol and hydrogen peroxide. The tolerance to these treatments was associated with decreased hydrogen peroxide levels and enhanced total peroxidase activity, enhanced content of osmoprotectants- proline and sucrose in transgenic plants. They showed higher retention of total chlorophyll and reduced TBARS in leaf disc assays with stress treatments, and decreased hydrogen peroxide accumulation in the stomatal guard cells when compared to their wild type counterparts. They also showed significantly enhanced fresh weight, relative water content, dry weight under stress. Treatment with sodium chloride resulted in enhanced expression of genes for Delta-pyrroline-5-carboxylase synthetase in leaves, and sucrose phosphate synthase, sucrose synthase and cellulose synthase A in the leaves and fibers of transgenic plants. The transgenic plants maintained normal seed development, fiber quality and cellulose content under stress.

Molecular cloning and characterization of five annexin genes from Indian mustard (Brassica juncea L. Czern and Coss)

Plant annexins constitute a multigene family having suggested roles in a variety of cellular processes including stress responses. We have isolated and characterized five different cDNAs of mustard, Brassica juncea (AnnBj1, AnnBj2, AnnBj3, AnnBj6 and AnnBj7) encoding annexin proteins using a RT-PCR/RACE-PCR based strategy. The predicted molecular masses of these annexins are approximately 36.0 kDa with acidic pIs. At the amino acid level, they share high sequence similarity with each other and with annexins from higher plants. Phylogenetic analysis revealed their evolutionary relationship with corresponding orthologous sequences in Arabidopsis and deduced proteins in various plant species. Expression analysis by semi-quantitative RT-PCR revealed that these genes are differentially expressed in various tissues. The expression patterns of these genes also showed regulation by various stress conditions such as exposure to signaling molecules, salinity and oxidative stress and wounding. Additionally, the in silico promoter analysis (of AnnBj1, AnnBj2 and AnnBj3) showed the presence of different cis-responsive elements that could respond to various stress conditions. These results indicate that AnnBj genes may play important roles in adaptation of plants to various environmental stresses.

Heterologous expression of Arabidopsis NPR1 (AtNPR1) enhances oxidative stress tolerance in transgenic tobacco plants

In Arabidopsis, NPR1 (non-expressor of pathogenesis related genes 1, AtNPR1) functions downstream of salicylic acid (SA) and modulates the SA mediated systemic acquired resistance. It is also involved in a cross talk with the jasmonate pathway that is essential for resistance against herbivores and necrotrophic pathogens. Overexpression of AtNPR1 in transgenic plants resulted in enhanced disease resistance. Recently, tobacco transgenic plants expressing AtNPR1 were shown to be tolerant to the early instars of Spodoptera litura (Meur et al., Physiol Plant 133:765-775, 2008). In this communication, we show that the heterologous expression of AtNPR1 in tobacco has also enhanced the oxidative stress tolerance. The transgenic plants exhibited enhanced tolerance to the treatment with methyl viologen. This tolerance was associated with the constitutive upregulation of PR1, PR2 (glucanase), PR5 (thaumatin like protein), ascorbate peroxidase (APX) and Cu(2+)/Zn(2+) superoxide dismutase (SOD). This is the first demonstration of the novel function of heterologous expression of AtNPR1 in oxidative stress tolerance in transgenic tobacco.

Transgenic tobacco and peanut plants expressing a mustard defensin show resistance to fungal pathogens

Defensins are small positively charged, antimicrobial peptides (approximately 5 kDa in size) and some of them exhibit potent antifungal activity. We have cloned the complete cDNA containing an ORF of 243 bp of a defensin of mustard. The deduced amino acid sequence of the peptide showed more than 90% identity to the amino acid sequence of the well-characterized defensins, RsAFP-1 and RsAFP-2 of Raphanus sativus. We have generated and characterized transgenic tobacco and peanut plants constitutively expressing the mustard defensin. Transgenic tobacco plants were resistant to the fungal pathogens, Fusarium moniliforme and Phytophthora parasitica pv. nicotianae. Transgenic peanut plants showed enhanced resistance against the pathogens, Pheaoisariopsis personata and Cercospora arachidicola, which jointly cause serious late leaf spot disease. These observations indicate that the mustard defensin gene can be deployed for deriving fungal disease resistance in transgenic crops.

Prokaryotic expression of a constitutively expressed Tephrosia villosa defensin and its potent antifungal activity

Plant defensins are small, highly stable, cysteine-rich antimicrobial peptides produced by the plants for inhibiting a broad-spectrum of microbial pathogens. Some of the well-characterized plant defensins exhibit potent antifungal activity on certain pathogenic fungal species only. We characterized a defensin, TvD1 from a weedy leguminous herb, Tephrosia villosa. The open reading frame of the cDNA was 228 bp, which codes for a peptide with 75 amino acids. Expression analyses indicated that this defensin is expressed constitutively in T. villosa with leaf, stem, root, and seed showing almost similar levels of high expression. The recombinant peptide (rTvD1), expressed in the Escherichia coli expression system, exhibited potent in vitro antifungal activity against several filamentous soil-borne fungal pathogens. The purified peptide also showed significant inhibition of root elongation in Arabidopsis seedlings, subsequently affecting the extension of growing root hairs indicating that it has the potential to disturb the plant growth and development.

Characterization of Bacillus thuringiensis strain DOR4 toxic to castor semilooper Achaea janata: proteolytic processing and binding of toxins to receptors

We have isolated a strain of Bacillus thuringiensis (Bt) from Indian soil samples that was shown to be toxic to Achaea janata larvae. The isolate, named B. thuringiensis DOR4, serotypically identified with the standard subspecies kurstaki (H3a3b3c) and produced bipyramidal inclusions along with an amorphous type. Although the plasmid pattern of DOR4 was different from that of the reference strain, a crystal protein profile showed the presence of two major bands (130 and 65 kDa) similar to those of Bt subsp. kurstaki HD-1. To verify the cry gene content of DOR4, triplex PCR analysis was performed; it showed amplification of the cry1C gene in addition to cry1Aa, cry1Ac, cry2A, and cry2B genes, but not the cry1Ab gene. RT-PCR analysis showed the expression of cry1Aa and cry1Ac genes. In vitro proteolysis of DOR4 protoxin with midgut extract generated products of different sizes. Zymogram analysis of DOR4 protoxin as substrate pointed to a number of distinct proteases that were responsible for activation of protoxins. Furthermore, toxin overlay analysis revealed the presence of multiple toxin-binding proteins in midgut epithelium. Based on all these characterizations, we suggest that the Bt DOR4 strain can be exploited for an A. janata control program.

A duplicated coxI gene is associated with cytoplasmic male sterility in an alloplasmic Brassica juncea line derived from somatic hybridization with Diplotaxis catholica

A cytoplasmic male sterile (CMS) line of Brassica juncea was derived by repeated backcrossing of the somatic hybrid (Diplotaxis catholica + B. juncea) to B. juncea. The new CMS line is comparable to euplasmic lines for almost all characters, except for flowers which bear slender, needle-like anthers with aborted pollen. Detailed Southern analysis revealed two copies of coxI gene in the CMS line. One copy, coxI-1 is similar to the coxI gene of B. juncea, whereas the second copy, coxI-2 is present in a novel rearranged region. Northern analysis with eight mitochondrial gene probes showed altered transcript pattern only for the coxI gene. Two transcripts of 2.0 and 2.4 kb, respectively, were detected in the CMS line. The novel 2.4 kb transcript was present in floral bud tissue but absent in the leaf tissue. In plants where male sterility broke down under high temperature during the later part of the growing season, the 2.4 kb coxI transcript was absent, which suggested its association with the CMS. The two coxI genes from the CMS line showed two amino acid changes in the coding region. The novel coxI gene showed unique repeats in the 5' region suggesting recombination of mitochondrial genomes of the two species. The possible role of the duplicated coxI gene in causing male sterility is discussed.

Characterization of Bacillus thuringiensis Cry toxin binding novel GPI anchored aminopeptidase from fat body of the moth Spodoptera litura

Aminopeptidase N (APN) isoforms were identified as candidate receptors for Bacillus thuringiensis Cry toxins from the midgut of several insect species. In this study a partial cDNA encoding aminopeptidase (slfbAPN) was cloned from fat body of the moth Spodoptera litura. In the deduced amino acid sequence the characteristic metallopeptidase sequences, HEXXHX(18)E and GAMENWG were conserved but the sequence showed only 33-39% identity to other insect APNs, which were also reported to be Cry toxin receptors. The presence of a putative GPI anchor signal sequence at the C-terminus indicated that it is a membrane-anchored protein. The slfbAPN expression was restricted to the fat body as suggested by northern blot analysis of different tissues. Biochemical analyses including immunoblotting, ligand blotting and lectin blotting, demonstrated that slfbAPN is a membrane-anchored glycoprotein in the fat body and it binds to Cry toxins.

Genetic transformation of peanut (Arachis hypogaea L.) using cotyledonary node as explant and a promoterless gus::nptII fusion gene based vector

We have generated putative promoter tagged transgenic lines in Arachis hypogaea cv JL-24 using cotyledonary node (CN) as an explant and a promoterless gus::nptII bifunctional fusion gene mediated by Agrobacterium transformation. MS medium fortified with 6-benzylaminopurine (BAP) at 4mg/l in combination with 0.1 mg/l alpha -napthaleneacetic acid (NAA) was the most effective out of the various BAP and NAA combinations tested in multiple shoot bud formation. Parameters enhancing genetic transformation viz. seedling age, Agrobacterium genetic background and co-cultivation periods were studied by using the binary vector p35SGUSINT. Genetic transformation with CN explants from 6-day-old seedlings co-cultivated with Agrobacterium GV2260 strain for 3 days resulted in high kanamycin resistant shoot induction percentage (45%); approximately 31% transformation frequency was achieved with p35S GUSINT in beta-glucuronidase (GUS) assays. Among the in vivo GUS fusions studied with promoterless gus::nptII construct, GUS-positive sectors occupied 38% of the total transient GUS percentage. We have generated over 141 putative T 0 plants by using the promoterless construct and transferred them to the field. Among these, 82 plants survived well in the green house and 5 plants corresponding to 3.54% showed stable integration of the fusion gene as evidenced by GUS, polymerase chain reaction (PCR) and Southern blot analyses. Twenty-four plants were positive for GUS showing either tissue-specific expression or blue spots in at least one plant part. The progeny of 15 T 0 plants indicated Mendelian inheritance pattern of segregation for single-copy integration. The tissue-specific GUS expression patterns were more or less similar in both T 0 and corresponding T 1 progeny plants. We present the differential patterns of GUS expression identified in the putative promoter-tagged transgenic lines in the present communication.

Homeotic-like modification of stamens to petals is associated with aberrant mitochondrial gene expression in cytoplasmic male sterile Ogura Brassica juncea

We have previously reported correction of severe leaf chlorosis in the cytoplasmic male sterile Ogura (also called Ogu) Brassica juncea line carrying Ogura cytoplasm by plastid substitution via protoplast fusion. Two cybrids obtained from the fusion experiment, Og1 and Og2, were green and carried the plastid genome of B. juncea cv. RLM198. While Og1 displayed normal flower morphology comparable to that of its euplasmic B. juncea counterpart except for sterile anthers, Og2 retained homeotic-like floral modification of stamens to petal-like structures and several other floral deformities observed in the chlorotic (Ogu) B. juncea cv. RLM198 (or OgRLM). With respect to the mitochondrial genome, Og1 showed 81% genetic similarity to the fertile cultivar RLM while Og2 showed 93% similarity to OgRLM. In spite of recombination and rearrangements in the mitochondrial genomes in the cybrids, expression patterns of 10 out of 11 mitochondrial genes were similar in all the three CMS lines; the only exception was atp6, whose expression was altered. While Og1 showed normal atp6 transcript similar to that in RLM, in Og2 and OgRLM weak expression of a longer transcript was detected. These results suggest that the homeotic-like changes in floral patterning leading to petaloid stamens in Og2 and OgRLM may be associated with aberrant mitochondrial gene expression.

Cloning, characterization and antifungal activity of defensin Tfgd1 from Trigonella foenum-graecum L

Defensins are small cysteine rich peptides with a molecular mass of 5-10 kDa and some of them exhibit potent antifungal activity. We have cloned the coding region of a cDNA of 225 bp cysteine rich defensin, named as Tfgd1, from the legume Trigonella foenum-graecum. The amino acid sequence deduced from the coding region comprised 74 amino acids, of which the N-terminal 27 amino acids constituted the signal peptide and the mature peptide comprised 47 amino acids. The protein is characterized by the presence of eight cysteine resisdues, conserved in the various plant defensins forming four disulphide bridges, which stabilize the mature peptide. The recombinant protein expressed in E coli exhibited antifungal activity against the broad host range fungus, Rhizoctonia solani and the peanut leaf spot fungus, Phaeoisariopsis personata.

Modification of erucic acid content in Indian mustard (Brassica juncea) by up-regulation and down-regulation of the Brassica juncea FAT TY ACID ELONGATION1 (BjFAE1) gene

In Brassicas, the Fatty Acid Elongation1 (FAE1) gene product, a 3-ketoacyl-CoA synthase, is the first in a 4-enzyme complex involved in the synthesis of erucic acid from oleic acid. The FAE1 homologue from Brassica juncea cv. Pusa Bold was cloned in a binary vector both in sense and antisense orientations under the control of the CaMV35S promoter. The recombinant binary vectors were used to transform B. juncea cv. RLM 198 via Agrobacterium tumefaciens. The presence of the transgene was confirmed by polymerase chain reaction and Southern hybridization. Northern and western analyses showed the expression of the gene and protein, respectively, in the transgenic plants. Analyses of the fatty acid profile of the seed oil from homozygous T4 generation seeds revealed that over-expression of the FAE1 gene caused a 36% increase in the percent of erucic acid (37-49% compared to 36% in untransformed control). The down-regulation of FAE1 caused an 86% decrease in the percent of erucic acid to as low as 5% in the seed oil of transgenic plants. Thus, it is clearly possible to alter erucic acid content of mustard by altering the expression level of the FAE 1 gene.

Cytoplasmic male sterility in alloplasmic Brassica juncea carrying Diplotaxis catholica cytoplasm: molecular characterization and genetics of fertility restoration

The present study was aimed at characterizing cytoplasmic male sterility (CMS) and identifying the fertility restorer gene for CMS (Diplotaxis catholica) Brassica juncea derived through sexual hybridization. The fertility restorer gene was identified by crossing the CMS line with progeny plants derived from somatic hybrids of B. juncea and D. cathoilca. The CMS line is comparable to the nuclear donor B. juncea in all respects except for flower and silique characteristics. In CMS plants, the flowers have smaller nectaries, and anthers are converted into petals or tubular structures. Gynoecium exhibits a crooked style and trilocular ovary. Seed fertility was reduced in the CMS line. Genetic segregation data indicated that a single, dominant, nuclear gene governs fertility restoration. Restored plants showed a high female fertility and lacked gynoecium abnormalities. In fertility-restored plants, petal development was found to be variable; some flowers had the normal number of four petals, while others had zero to three petals. Interestingly, the trilocular character of the ovary was found to co-segregate with CMS and became bilocular upon male-fertility restoration. Thus, this trait appears to be affected by the interaction of nuclear and mitochondrial (mt) genomes. Restriction fragment length polymorphism analysis indicated that mt-genome of D. catholica is highly divergent from that of B. juncea. However, in Northern analysis, out of eight mt genes studied, an altered transcript pattern was recorded for only atpA. In fertility-restored plants, the atpA transcript became shorter, thereby showing its association with CMS.

Agrobacterium-mediated transformation of cauliflower: optimization of protocol and development of Bt-transgenic cauliflower

A number of factors that are known to influence genetic transformation were evaluated to optimize Agrobacterium-mediated transformation of hypocotyl explants of cauliflower variety Pusa Snowball K-1. The binary vector p35SGUSINT mobilized into Agrobacterium strain GV2260 was used for transformation and transient GUS expression was used as the basis for identifying the most appropriate conditions for transformation. Explant age, preculture period, bacterial strain and density were found to be critical determinants of transformation efficiency. Using the optimized protocol, the synthetic cryIA(b) gene was mobilized into cauliflower. Molecular analyses of transgenics established the integration and expression of the transgene. Insect bioassays indicated the effectiveness of the transgene against infestation by diamondback moth (Plutella xylostella) larvae

Recombination between chloroplast genomes of Trachystoma ballii and Brassica juncea following protoplast fusion

We document here the presence of a recombinant plastome in a cytoplasmic male sterile (CMS) line of Brassica juncea developed from the somatic hybrid Trachystoma ballii + B. juncea. Restriction endonuclease digestion of the chloroplast (cp) DNA has revealed that the recombinant plastome gives rise to novel fragments in addition to the parent-specific fragments. Analysis of the 16S rRNA region by Southern hybridization shows no variation between B. juncea, T. ballii and the CMS line. The rbcL gene region of the recombinant plastome is identical to that in T. ballii. Analysis with probes for psbA and psbD using single and double DNA digests indicates that the hybridization patterns of the recombinant plastome are identical to those of the parents in digests obtained with some restriction enzymes, while novel bands hybridize to probes in other digests. In the psbA region, a B. juncea-specific PstI site and a T. ballii-specific EcoRI site are found in the recombinant plastome. The pshD region of the recombinant plastome contains a B. juncea-specific HindIII site and T. ballii-specific BamHI and HpaII sites. These results indicate the occurrence of intergenomic recombination between the chloroplasts of T. ballii and B. juncea in the somatic hybrid from which the CMS line was developed. The recombined plastome appears to be a mosaic of fragments specific to both parents and the recombination event has occurred in the single-copy regions. These recombinational events have not caused any imbalance in the recombinant plastome in terms of chloroplast-related functions, which have remained stable over generations.

Random chloroplast segregation and mitochondrial genome recombination in somatic hybrid plants of Diplotaxis catholica+Brassica juncea

Detailed molecular analysis of the somatic hybrid plants of Diplotaxis catholica+B. juncea indicated random chloroplast segregation. One of the five hybrid plants analyzed derived its chloroplasts from D. catholica and two hybrids had chloroplasts of B. juncea origin. Two hybrid plants maintained mixed population of chloroplasts. The mitochondrial (mt) genomes of the fusion partners had undergone recombinations. Occurrence of fragments specific to both the parents in HindIII digestion followed by atp 9 probing, as in hybrid DJ5, provided evidence for intergenomic mitochondrial recombination between D. catholica and B. juncea. Similar mt genome organization in two hybrids (DJ3 and DJ6) suggested that intergenomic recombination may be preferred at specific sites. Hybrid DJ1 had about 70% similarity to D. catholica in mt genome organization. mt genomes of hybrids DJ2, 3, 5, and 6 differed from B. juncea by 14.3-28%. The significance of these novel mt genome organizations in developing novel male sterility systems is discussed.

Transfer of Ogu cytoplasmic male sterility to Brassica juncea and improvement of the male sterile line through somatic cell fusion

Male sterility conferred by ogu cytoplasm of Raphanus sativus has been transferred to Brassica juncea cv 'RLM 198' from male-sterile B. napus through repeated backcrossing and selection. The male-sterile B. juncea is, however, highly chlorotic and late. It has low female (seed) fertility and small contorted pods. To rectify these defects, protoplasts of the male sterile were fused with normal 'RLM 198' (green, self fertile). Four dark green, completely male-sterile plants were obtained and identified as putative cybrids. All the plants were backcrossed three times with 'RLM 198'. Mitochondrial and chloroplast DNA analysis of backcross progeny confirmed hybridity of the cytoplasm. The restriction pattern of the chloroplast DNA of progeny plants of three cybrids (Og 1, Og 2, Og 3) was similar to that of the green self-fertile 'RLM 198' and indicated that the correction of chlorosis resulted from chloroplast substitution. The chloroplast DNA of the lone progeny plant of the fourth cybrid (Og 10) could not be analyzed because the plant was stunted and had only a few leaves. When total cellular DNA was probed with mitochondrial probes coxI and atpA it was found that the cybrids had recombinant mitochondria. The chlorosis-corrected plants were early flowering and had vastly improved seed fertility.

Diplotaxis catholica + Brassica juncea somatic hybrids: molecular and cytogenetic characterization

Intergeneric somatic hybrids Diplotaxis catholica (2n=18) + Brassica juncea (2n=36) were produced by fusing mesophyll protoplasts of the former and hypocotyl protoplasts of the latter using polyethylene glycol. Out of 52 somatic embryos, 24 produced plants of intermediate morphology. Cytological analysis of 16 plants indicated that 15 were symmetric hybrids carrying 54 chromosomes, the sum of the parental chromosome numbers. One hybrid was asymmetric with 45 chromosomes. Nuclear hybridity of five putative hybrids was confirmed by the Southern hybridization pattern of full length 18s-25s wheat nuclear rDNA probe which revealed the presence of Hind III fragments characteristic of both the parental species. The hybridization pattern of mitochondria specific gene probe cox I indicated that three of the hybrids carried B. juncea mitochondria and one carried mitochondria of D. catholica. Presence of novel 3.5 kb Hind III and 4.8 kb Bgl II fragments suggested the occurrence of mtDNA recombination in one of the hybrids. The hybrids were pollen sterile. However, seeds were obtained from most of the hybrids by back crossing with B. juncea.