Genetic and Pathogenic Variability of Indian Strains of <Emphasis Type="Italic">Xanthomonas campestris</Emphasis> pv. <Emphasis Type="Italic">campestris</Emphasis> Causing Black Rot Disease in Crucifers

Xanthomonas campestris pv. campestris (Pammel) Dowson (Xcc) causing black rot of crucifers is a serious disease in India and causes >50% crop losses in favorable environmental conditions. Pathogenic variability of Xcc, X. oryzae pv. oryzae (Xoo), and X. axonopodis pv. citri (Xac) were tested on 19 cultivars of cruciferae including seven Brassica spp. viz., B. campestris, B. carinata, B. juncea, B. napus, B. nigra, B. oleracea and B. rapa, and Raphanus sativus for two consecutive years viz., 2007–2008 and 2008–2009 under field conditions at Indian Agricultural Research Institute, New Delhi. Xcc (22 strains) and other species of Xanthomonas (2 strains), they formed three distinct groups of pathogenic variability i.e., Group 1, 2, and 3 under 50% minimum similarity coefficient. All strains of Xcc clustered under Groupl except Xcc-C20. The strains of Xcc further clustered in 6 subgroups viz., A, B, C, D, E, and F based on diseases reaction on host. Genetic variability of 22 strains of Xcc was studied by using Rep-PCR (REP-, BOX- and ERIC-PCR) and 10 strains for hrp (hypersensitive reaction and pathogenecity) gene sequence analysis. Xcc strains comprised in cluster 1, Xac under cluster 2, while Xoo formed separate cluster 3 based on >50% similarity coefficient. Cluster 1 was further divided into 8 subgroups viz., A, B, C, D, E, F, G, and H at 75% similarity coefficient. The hrpF gene sequence analysis also showed distinctness of Xcc strains from other Xanthomonads. In this study, genetic and pathogenic variability in Indian strains of Xcc were established, which will be of immense use in the development of resistant genotypes against this bacterial pathogen.     

Identification of genes differentially expressed in cauliflower associated with resistance to <Emphasis Type="Italic">Xanthomonas campestris</Emphasis> pv. <Emphasis Type="Italic">campestris</Emphasis>

Black rot, caused by Xanthomonas campestris pv. campestris (Pammel) Dowson (Xcc), is one of the most damaging diseases of cauliflower and other crucifers. In order to investigate the molecular resistance mechanisms and to find the genes related to black rot resistance in cauliflower, a suppression subtractive hybridization (SSH) cDNA library was constructed using resistant line C712 and its susceptible near-isogenic line C731 as tester and driver, respectively. A total of 280 clones were obtained from the library by reverse northern blotting. Sequencing analysis and homology searching showed that these clones represent 202 unique sequences. The library included many defense/disease-resistant related genes, such as plant defensin gene PDF1.2, lipid transfer protein, thioredoxin h. Gene expression profiles of 12 genes corresponding to different functional categories were monitored by real-time RT-PCR. The results showed that the expression induction of these genes in the susceptible line C712 in response to Xcc was quicker and more intense, while in C731 the reaction was delayed and limited. Our results imply that these up-regulated genes might be involved in cauliflower responses against Xcc infection. Information obtained from this study could be used to understand the molecular mechanisms of disease response in cauliflower under Xcc stress.     

RFLP mapping of loci controlling self-incompatibility in <Emphasis Type="Italic">Brassica campestris</Emphasis> and their comparative mapping with <Emphasis Type="Italic">B. napus</Emphasis> and <Emphasis Type="Italic">B. oleracea</Emphasis>

RFLP analysis of a cDNA probe SLG6, governing self incompatibility (SI) in Brassica oleracea, using a recombinant inbred population of Brassica campestris followed by genetic linkage analysis led to the detection of two marker loci, SLG6a and SLG6b controlling SI. SLG6a was mapped in linkage group (LG) 9 and was flanked by the RFLP markers ec4f10 (6.4 cM) and wg5b9 (4.2 cM). SLG6b positioned in LG 2 and was flanked by the RFLP markers wg2d11 (9.9 cM) and ec4e7 (26.9 cM). These results indicated the scope of marker-aided introgression of these genes into self-compatible genotypes for production of SI lines suitable for hybridization in B. campestris. Comparative mapping of LG 9 containing SLG6b with corresponding linkage groups of B. oleracea (BO 2) and B. napus (BN 16) led to the detection of small homologous regions with SLG6 locus linked with another RFLP locus. This evidenced for homology of the SLG genes across Brassica species and possibility of using any single cloned SLG gene for development of SI lines in any Brassica species.     

Functional analysis of <Emphasis Type="Italic">Xa3/Xa26</Emphasis> family members in rice resistance to <Emphasis Type="Italic">Xanthomonas</Emphasis><Emphasis Type="Italic">oryzae</Emphasis> pv. <Emphasis Type="Italic">oryzae</Emphasis>

Plant disease resistant (R) genes are frequently clustered in the genome. The diversity of members in a complex R-gene family may provide variation in resistance specificity. Rice Xa3/Xa26, conferring resistance to Xanthomonas oryzae pv. oryzae (Xoo) encodes a leucine-rich repeat (LRR) receptor kinase-type protein and belongs to a multigene family, consisting of Xa3/Xa26, MRKa, MRKc and MRKd in rice cultivar Minghui 63. MRKa and MRKc are intact genes, while MRKd is a pseudogene. Complementary analyses showed that MRKa and MRKc could not mediate resistance to Xoo when regulated by their native promoters, but MRKa not MRKc conferred partial resistance to Xoo when regulated by a strong constitutive promoter. Plants carrying truncated XA3/XA26, which lacked the kinase domain, were compromised in their resistance to Xoo. However, the kinase domain of MRKa could partially restore the function of the truncated XA3/XA26 in resistance. MRKa and MRKc showed similar expression pattern as Xa3/Xa26, which expressed only in the vascular systems of different tissues. The expressional characteristic of MRKa and MRKc perfectly fits the function of genes conferring resistance to Xoo, a vascular pathogen. These results suggest that although MRKa and MRKc cannot mediate bacterial blight resistance nowadays, they may be once effective genes for Xoo resistance. Their expressional characteristic and sequence similarity to Xa3/Xa26 will provide templates for generating novel recognition specificity to face the evolution of Xoo. In addition, both LRR and kinase domains encoded by Xa3/Xa26 and MRKa are the functional determinants and MRKa-mediated resistance is dosage-dependent. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

<Emphasis Type="Italic">smyd1</Emphasis> and <Emphasis Type="Italic">smyd2</Emphasis> are expressed in muscle tissue in <Emphasis Type="Italic">Xenopus laevis</Emphasis>

Epigenetic modifications of histone play important roles for regulation of cell activity, such as cell division, cell death, and cell differentiation. A SET domain consisting of about 130 amino acids has lysine methyltransferase activity in the presence of the cosubstrate S-adenosyl-methionine. More than 60 SET domain-containing proteins have been predicted in various organisms. One of them, the SMYD family genes which contain a SET domain and a zinc-finger MYND domain are reported to regulate cell cycle and muscle formation. Here we examined the expression and function of smyd1 and 2 in Xenopus. smyd1 and 2 were expressed in various muscle tissues. While smyd1 expression was observed mainly in cardiac muscle and skeletal muscle, smyd2 expression was done abundantly in skeletal muscle and face region. Moreover, by loss-of-function experiments using antisense morpholino oligonucleotides, it was suggested that smyd1 and 2 related to muscle cells differentiation.