Small RNAs, such as microRNAs (miRNAs) and small interfering RNAs (siRNAs), play crucial roles in post-transcriptional gene silencing (PTGS) in eukaryotes. Small RNAs function cell-autonomously as well as non-cell-autonomously. It has been well characterized that pathogenic fungi secrete some effector molecules facilitating their infection into plants. However, it is unclear whether molecules produced in plant cells are able to move into fungal cells during infection. To test if small RNAs generated from plant cells can move to fungal cells during infection, we generated transgenic Arabidopsis and rice plants expressing siRNAs targeting GFP gene generated from double-stranded RNA interference (dsRNAi) constructs for GFP gene. And then these transgenic plants were inoculated with transgenic rice blast fungus, Magnaporthe oryzae, expressing GFP transgene. Here, we showed that ectopic expression of siRNAs targeting GFP gene in transgenic plants significantly suppressed GFP expression in rice blast fungi inoculated, indicating that small RNA molecules generated in plant cells can move into infected fungal cells and efficiently degrade fungal GFP transcripts. Our results would provide a new small RNA-based strategy for the development of resistant crops against fungal pathogens.

To identify novel signaling components involved in regulation of plant responses to phosphate (Pi) starvation, we screened an Arabidopsis T-DNA activation tagging library for mutants with altered Pi-starvation responses. Here, we report the identification and characterization of novel activation-tagged mutant involved in Pi starvation signaling in Arabidopsis. The hpd (hypersensitive to Pi deficiency) mutant exhibits enhanced phosphate uptake and altered root architectural change under Pi starvation compared to wild type. Expression analysis of auxin-responsive DR5::GUS reporter gene in hpd mutant indicated that both auxin biosynthesis and auxin translocation under Pi starvation are suppressed in hpd mutant plants. Impaired auxin translocation in roots of hpd mutant was attributable to abnormal root architecture changes in Pi starvation conditions. Mis-regulation of auxin translocation in hpd mutant was further confirmed by analysis of expression patterns of auxin efflux carrier proteins, PIN-FORMED (PIN) 1, 2, and 3 fused with GFP. Not only expression levels but also expression domains of PIN proteins were altered in hpd mutant in response to Pi starvation. Molecular genetic analysis of hpd mutant revealed that the mutant phenotype is caused by the lesion in ENHANCED SILENCING PHENOTYPE4 (ESP4) gene whose function is proposed in mRNA 3’-end processing. The results propose that mRNA processing plays crucial roles in Pi homeostasis as well as developmental reprograming in response to Pi deprivation in Arabidopsis.

In order to adapt to various environmental stresses, plants have employed diverse regulatory mechanisms of gene expression. Epigenetic changes, such as DNA methylation and histone modifications play an important role in gene expression regulation under stress condition. It has been known that some of epigenetic modifications are stably inherited after mitotic and meiotic cell divisions, which is known as stress memory. To understand molecular mechanisms underlying stress memory mediated by epigenetic modifications, we developed Arabidopsis suspension-cultured cell lines adapted to high salt by stepwise increases in the NaCl concentration up to 120 mM. Adapted cell line to 120 mM NaCl, named A120, exhibited enhanced salt tolerance compared to unadapted control cells (A0). Moreover, the salt tolerance of A120 cell line was stably maintained even in the absence of added NaCl, indicating that the salt tolerance of A120 cell line was memorized even after the stress is relieved. By using salt adapted and stress memorized cell lines, we intend to analyze the changes of DNA methylation, histone modification, transcriptome, and proteome to understand molecular mechanisms underlying stress adaptation as well as stress memory in plants.

Small RNAs including microRNAs (miRNAs) and small interfering RNAs (siRNAs) play crucial roles in post-transcriptional gene silencing (PTGS) in eukaryotes. Small RNAs function cell-autonomously as well as non-cell-autonomously. It has been well characterized that pathogenic fungi secrete some effector molecules, which facilitate their infection into plants. However, it is not clear whether molecules in plant cells are able to move into fungal cells during infection. To test if small RNAs generated from plant cells can also move to fungal cells during infection, we generated transgenic Arabidopsis and rice plants ectopically expressing either double-stranded RNA interference (dsRNAi) or artificial miRNA (amiRNA) constructs targeting GFP gene. And then these transgenic plants were inoculated with transgenic rice blast fungus, Magnaporthe oryzae, expressing GFP transgene. Here, we showed that ectopic expression of both dsRNAi and amiRNA targeting GFP gene in transgenic plants significantly suppressed GFP expression in rice blast fungi inoculated, indicating that small RNA molecules generated in plant cells can move into infected fungal cells and efficiently degrade fungal GFP transcripts. Our results would provide a new small RNA-based strategy for the development of resistant crops against fungal pathogens.