Comparative Transcriptional Profiling of Melatonin Synthesis and Catabolic Genes Indicates the Possible Role of Melatonin in Developmental and Stress Responses in Rice

As a well-known animal hormone, melatonin (N-acetyl-5-methoxytryptamine) is also involved in multiple plant biological processes, especially in various stress responses. Rice is one of the most important crops, and melatonin is taken in by many people everyday from rice. However, the transcriptional profiling of melatonin-related genes in rice is largely unknown. In this study, the expression patterns of 11 melatonin related genes in rice in different periods, tissues, in response to different treatments were synthetically analyzed using published microarray data. These results suggest that the melatonin-related genes may play important and dual roles in rice developmental stages. We highlight the commonly regulation of rice melatonin-related genes by abscisic acid (ABA), jasmonic acid (JA), various abiotic stresses and pathogen infection, indicating the possible role of these genes in multiple stress responses and underlying crosstalks of plant hormones, especially ABA and JA. Taken together, this study may provide insight into the association among melatonin biosynthesis and catabolic pathway, plant development and stress responses in rice. The profile analysis identified candidate genes for further functional characterization in circadian rhythm and specific stress responses

A Novel Manganese Efflux System, YebN, Is Required for Virulence by Xanthomonas oryzae pv. oryzae

Manganese ions (Mn2+) play a crucial role in virulence and protection against oxidative stress in bacterial pathogens. Such pathogens appear to have evolved complex mechanisms for regulating Mn2+ uptake and efflux. Despite numerous studies on Mn2+ uptake, however, only one efflux system has been identified to date. Here, we report on a novel Mn2+ export system, YebN, in Xanthomonas oryzae pv. oryzae (Xoo), the causative agent of bacterial leaf blight. Compared with wild-type PXO99, the yebN mutant was highly sensitive to Mn2+ and accumulated high concentrations of intracellular manganese. In addition, we found that expression of yebN was positively regulated by Mn2+ and the Mn2+-dependent transcription regulator, MntR. Interestingly, the yebN mutant was more tolerant to methyl viologen and H2O2 in low Mn2+ medium than PXO99, but more sensitive in high Mn2+ medium, implying that YebN plays an important role in Mn2+ homoeostasis and detoxification of reactive oxygen species (ROS). Notably, deletion of yebN rendered Xoo sensitive to hypo-osmotic shock, suggesting that YebN may protect against such stress. That mutation of yebN substantially reduced the Xoo growth rate and lesion formation in rice implies that YebN could be involved in Xoo fitness in host. Although YebN has two DUF204 domains, it lacks homology to any known metal transporter. Hence, this is the first report of a novel metal export system that plays essential roles in hypo-osmotic and oxidative stress, and virulence. Our results lay the foundations for elucidating the complex and fascinating relationship between metal homeostasis and host-pathogen interactions

Tropical pasture research in China: Present and future

En China, la investigacion en pasturas tropicales se enfoca principalmente hacia introduccion y evaluacion, agronomia de forrajeras, seleccion y tecnicas de cultivo. Se han seleccionado varias var., las cuales se han recomendado para uso comercial como Stylosanthes guianensis CIAT 184, Brachiaria decumbens CIAT 606, Andropogon gayanus CIAT 621 y Pennisetum purpureum. Tambien se han logrado avances en el desarrollo de pasturas con mejores tecnicas de establecimiento y manejo y con la seleccion de asociaciones de gramineas y leguminosas. Actualmente, South China Academy of Tropical Crops desarrolla actividades en 5 areas: 1) la recoleccion, introduccion, evaluacion y seleccion de germoplasma de pasturas tropicales, en colaboracion con CIAT; 2) el cultivo y la utilizacion de Leucaena leucocephala, con la creacion de un banco de germoplasma con 72 accesiones de L. leucocephala y otras 8 especies del genero; 3) el desarrollo de pasturas tropicales, particularmente en la isla de Hainan; 4) la produccion de semilla de pasturas tropicales en la region sur de Hainan, donde prevalecen temp. altas y buena iluminacion; 5) la investigacion sobre la utilizacion de harina integral de forrajeras tropicales en la alimentacion de cerdos y aves de corral, en este momento solamente con la leguminosa forrajera Stylosanthes spp. (Extracto

High Concentration of Melatonin Regulates Leaf Development by Suppressing Cell Proliferation and Endoreduplication in Arabidopsis

N-acetyl-5-methoxytryptamine (Melatonin), as a crucial messenger in plants, functions in adjusting biological rhythms, stress tolerance, plant growth and development. Several studies have shown the retardation effect of exogenous melatonin treatment on plant growth and development. However, the in vivo role of melatonin in regulating plant leaf growth and the underlying mechanism are still unclear. In this study, we found that high concentration of melatonin suppressed leaf growth in Arabidopsis by reducing both cell size and cell number. Further kinetic analysis of the fifth leaves showed that melatonin remarkably inhibited cell division rate. Additionally, flow cytometic analysis indicated that melatonin negatively regulated endoreduplication during leaf development. Consistently, the expression analysis revealed that melatonin regulated the transcriptional levels of key genes of cell cycle and ribosome. Taken together, this study suggests that high concentration of melatonin negatively regulated the leaf growth and development in Arabidopsis, through modulation of endoreduplication and the transcripts of cell cycle and ribosomal key genes