Chitin-induced systemic disease resistance in rice requires both OsCERK1 and OsCEBiP and is mediated via perturbation of cell-wall biogenesis in leaves

Chitin is a well-known elicitor of disease resistance and its recognition by plants is crucial to perceive fungal infections. Chitin can induce both a local immune response and a systemic disease resistance when provided as a supplement in soils. Unlike local immune responses, it is poorly explored how chitin-induced systemic disease resistance is developed. In this study, we report the systemic induction of disease resistance against the fungal pathogen Bipolaris oryzae by chitin supplementation of soils in rice. The transcriptome analysis uncovered genes related to cell-wall biogenesis, cytokinin signaling, regulation of phosphorylation, and defence priming in the development of chitin-induced systemic response. Alterations of cell-wall composition were observed in leaves of rice plants grown in chitin-supplemented soils, and the disease resistance against B. oryzae was increased in rice leaves treated with a cellulose biosynthesis inhibitor. The disruption of genes for lysin motif (LysM)-containing chitin receptors, OsCERK1 (Chitin elicitor receptor kinase 1) and OsCEBiP (Chitin elicitor-binding protein), compromised chitin-induced systemic disease resistance against B. oryzae and differential expression of chitin-induced genes found in wild-type rice plants. These findings suggest that chitin-induced systemic disease resistance in rice is caused by a perturbation of cell-wall biogenesis in leaves through long-distance signalling after local recognition of chitins by OsCERK1 and OsCEBiP.

Stochastic Binding Dynamics of a Photoswitchable Single Supramolecular Complex

In this work, a real-time precise electrical method to directly monitor the stochastic binding dynamics of a single supramolecule based on the host-guest interaction between a cyclodextrin and an azo compound is reported. Different intermolecular binding states during the binding process are distinguished by conductance signals detected from graphene-molecule-graphene single-molecule junctions. In combination with theoretical calculations, the reciprocating and unidirectional motions in the trans form as well as the restrained reciprocating motion in the cis form due to the steric hindrance is observed, which could be reversibly switched by visible and UV irradiation. The integration of individual supramolecules into nanocircuits not only offers a facile and effective strategy to probe the dynamic process of supramolecular systems, but also paves the way to construct functional molecular devices toward real applications such as switches, sensors, and logic devices.

Activation of DNA Transposons and Evolution of piRNA Genes Through Interspecific Hybridization in Xenopus Frogs

Interspecific hybridization between two closely related species sometimes resulted in a new species with allotetraploid genomes. Many clawed frog species belonging to the Xenopus genus have diverged from the allotetraploid ancestor created by the hybridization of two closely related species with the predicted L and S genomes. There are species-specific repeated sequences including transposable elements in each genome of organisms that reproduce sexually. To understand what happened on and after the hybridization of the two distinct systems consisting of repeated sequences and their corresponding piRNAs, we isolated small RNAs from ovaries and testes of three Xenopus species consisting of allotetraploid X. laevis and X. borealis and diploid X. tropicalis as controls. After a comprehensive sequencing and selection of piRNAs, comparison of their sequences showed that most piRNA sequences were different between the ovaries and testes in all three species. We compared piRNA and genome sequences and specified gene clusters for piRNA expression in each genome. The synteny and homology analyses showed many distinct piRNA clusters among the three species and even between the two L and/or S subgenomes, indicating that most clusters of the two allotetraploid species changed after hybridization. Moreover, evolutionary analysis showed that DNA transposons including Kolobok superfamily might get activated just after hybridization and then gradually inactivated. These findings suggest that some DNA transposons and their piRNAs might greatly influence allotetraploid genome evolution after hybridization.