Signatures of adaptation to a monocot host in the plant-parasitic cyst nematode Heterodera sacchari.

Interactions between plant-parasitic nematodes and their hosts are mediated by effectors, i.e. secreted proteins that manipulate the plant to the benefit of the pathogen. To understand the role of effectors in host adaptation in nematodes, we analysed the transcriptome of Heterodera sacchari, a cyst nematode parasite of rice (Oryza sativa) and sugarcane (Saccharum officinarum). A multi-gene phylogenetic analysis showed that H. sacchari and the cereal cyst nematode Heterodera avenae share a common evolutionary origin and that they evolved to parasitise monocot plants from a common dicot-parasitic ancestor. We compared the effector repertoires of H. sacchari with those of the dicot parasites Heterodera glycines and Globodera rostochiensis to understand the consequences of this transition. While, in general, effector repertoires are similar between the species, comparing effectors and non-effectors of H. sacchari and G. rostochiensis shows that effectors have accumulated more mutations than non-effectors. Although most effectors show conserved spatiotemporal expression profiles and likely function, some H. sacchari effectors are adapted to monocots. This is exemplified by the plant-peptide hormone mimics, the CLAVATA3/EMBRYO SURROUNDING REGION-like (CLE) effectors. Peptide hormones encoded by H. sacchari CLE effectors are more similar to those from rice than those from other plants, or those from other plant-parasitic nematodes. We experimentally validated the functional significance of these observations by demonstrating that CLE peptides encoded by H. sacchari induce a short root phenotype in rice, whereas those from a related dicot parasite do not. These data provide a functional example of effector evolution that co-occurred with the transition from a dicot-parasitic to a monocot-parasitic lifestyle.BBSR

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In vitro life cycle of Heterodera sacchari on Pluronic gel

This paper presents studies on the life cycle of Heterodera sacchari under in vitro conditions. Pluronic gel was used as a medium for growth of H. sacchari. The life cycle was completed in 7-9 weeks on rice (Oryza sativa, 'Nipponbare'). After infection, juveniles developed and reached the reproducing adult female stage at 25 days post inoculation (dpi). At 35 dpi, all females produced eggs in various numbers. Some females were translucent and eggs inside could be counted. At 49 dpi females started to tan and developed into dark brown cysts. Hatching of H. sacchari juveniles from cysts could be stimulated by 3 mM ZnCl2 but not by rice root exudates. The in vitro culture of H. sacchari on Pluronic gel can be used efficiently to collect post-infective nematode/host samples at different time points for various studies and to screen different rice cultivars for resistance/susceptibility.</p

In vitro life cycle of Heterodera sacchari on Pluronic gel

This paper presents studies on the life cycle of Heterodera sacchari under in vitro conditions. Pluronic gel was used as a medium for growth of H. sacchari. The life cycle was completed in 7-9 weeks on rice (Oryza sativa, 'Nipponbare'). After infection, juveniles developed and reached the reproducing adult female stage at 25 days post inoculation (dpi). At 35 dpi, all females produced eggs in various numbers. Some females were translucent and eggs inside could be counted. At 49 dpi females started to tan and developed into dark brown cysts. Hatching of H. sacchari juveniles from cysts could be stimulated by 3 mM ZnCl2 but not by rice root exudates. The in vitro culture of H. sacchari on Pluronic gel can be used efficiently to collect post-infective nematode/host samples at different time points for various studies and to screen different rice cultivars for resistance/susceptibility.</p

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Not AvailableRice root knot nematode, Meloidogyne graminicola is one of the important constraints in the major rice growing areas of Asia especially in India. In the present study, resistance / susceptibility of NRRI released rice varieties/hybrids against M. graminicola were assessed through root gall index scoring. Development of nematodes inside the galls in the resistant and susceptible varieties were also assessed. Among the 115 NRRI varieties screened against rice root knot nematode, 20 varieties were reported to exhibit high susceptibility (gall index - 5), 68 varieties recorded susceptible reaction (gall index - 4) and 27 varieties registered moderately resistant reaction (gall index - 3) when evaluated under pot conditions. Examination of the moderately resistant varieties revealed less number of nematode penetration and female development in it with longer period of life cycle compared to susceptible varieties. Assured varieties recorded in the present study might be useful for breeding of hybrid rice for the nematode managementNot Availabl

Genetic Diversity and Streptomycin Sensitivity in <i>Xanthomonas axonopodis</i> pv. <i>punicae</i> Causing Oily Spot Disease in Pomegranates

Xanthomonas axonopodis pv. punicae (Xap) causes bacterial blight disease in pomegranates, often leading to 60–80% economic loss. In absence of a suitable Xap-resistant variety, the near-monoculture of the susceptible variety, Bhagwa, has aggravated the problem further. In recent times, Xap has spread to different geographical regions, indicating the wide adaptability of the pathogen. Moreover, lower sensitivity of Xap towards streptocycline containing streptomycin sulphate and tetracycline sulphate (9:1) under field conditions is frequently reported. Therefore, the current study was undertaken to assess the genetic variability of Xap isolates using SSR markers, their in vitro sensitivity towards streptomycin was evaluated, and the probable molecular basis of acquired resistance was studied. Two highly diverse isolates showed extreme differences in their pathogenicity, indicating the highly evolving nature of the pathogen. Moreover, all the isolates showed less than 50% growth inhibition on media containing 1500 µg/mL streptomycin, indicating a lower level of antibiotic sensitivity. On the molecular level, 90% of the isolates showed the presence of strA-strB genes involved in streptomycin metabolism. Additionally, G to A transitions were observed in the rpsL gene in some of the isolates. The molecular data suggest that horizontal gene transfer (strAB) and/or spontaneous gene mutation (in rpsL) could be responsible for the observed lower sensitivity of Xap towards streptomycin

Genetic Diversity and Streptomycin Sensitivity in Xanthomonas axonopodis pv. punicae Causing Oily Spot Disease in Pomegranates

Xanthomonas axonopodis pv. punicae (Xap) causes bacterial blight disease in pomegranates, often leading to 60&ndash;80% economic loss. In absence of a suitable Xap-resistant variety, the near-monoculture of the susceptible variety, Bhagwa, has aggravated the problem further. In recent times, Xap has spread to different geographical regions, indicating the wide adaptability of the pathogen. Moreover, lower sensitivity of Xap towards streptocycline containing streptomycin sulphate and tetracycline sulphate (9:1) under field conditions is frequently reported. Therefore, the current study was undertaken to assess the genetic variability of Xap isolates using SSR markers, their in vitro sensitivity towards streptomycin was evaluated, and the probable molecular basis of acquired resistance was studied. Two highly diverse isolates showed extreme differences in their pathogenicity, indicating the highly evolving nature of the pathogen. Moreover, all the isolates showed less than 50% growth inhibition on media containing 1500 &micro;g/mL streptomycin, indicating a lower level of antibiotic sensitivity. On the molecular level, 90% of the isolates showed the presence of strA-strB genes involved in streptomycin metabolism. Additionally, G to A transitions were observed in the rpsL gene in some of the isolates. The molecular data suggest that horizontal gene transfer (strAB) and/or spontaneous gene mutation (in rpsL) could be responsible for the observed lower sensitivity of Xap towards streptomycin

Signatures of adaptation to a monocot host in the plant‐parasitic cyst nematode Heterodera sacchari

Interactions between plant-parasitic nematodes and their hosts are mediated by effectors, i.e. secreted proteins that manipulate the plant to the benefit of the pathogen. To understand the role of effectors in host adaptation in nematodes, we analysed the transcriptome ofHeterodera sacchari, a cyst nematode parasite of rice (Oryza sativa) and sugarcane (Saccharum officinarum). A multi-gene phylogenetic analysis showed thatH. sacchariand the cereal cyst nematodeHeterodera avenaeshare a common evolutionary origin and that they evolved to parasitise monocot plants from a common dicot-parasitic ancestor. We compared the effector repertoires ofH. sacchariwith those of the dicot parasitesHeterodera glycinesandGlobodera rostochiensisto understand the consequences of this transition. While, in general, effector repertoires are similar between the species, comparing effectors and non-effectors ofH. sacchariandG. rostochiensisshows that effectors have accumulated more mutations than non-effectors. Although most effectors show conserved spatiotemporal expression profiles and likely function, someH. saccharieffectors are adapted to monocots. This is exemplified by the plant-peptide hormone mimics, the CLAVATA3/EMBRYO SURROUNDING REGION-like (CLE) effectors. Peptide hormones encoded byH. sacchariCLE effectors are more similar to those from rice than those from other plants, or those from other plant-parasitic nematodes. We experimentally validated the functional significance of these observations by demonstrating that CLE peptides encoded byH. sacchariinduce a short root phenotype in rice, whereas those from a related dicot parasite do not. These data provide a functional example of effector evolution that co-occurred with the transition from a dicot-parasitic to a monocot-parasitic lifestyle