Brown planthopper (BPH) is a notorious pest of rice plants attacking leaf sheaths and seriously affecting global rice production. However, how rice plants respond against BPH remains to be fully understood. To understand systems metabolic responses of rice plants to BPH infestation, we analyzed BPH-induced metabolic changes in leaf sheaths of both BPH-susceptible and resistant rice varieties using NMR-based metabonomics and measured expression changes of 10 relevant genes using quantitative real-time PCR. Our results showed that rice metabonome was dominated by more than 30 metabolites including sugars, organic acids, amino acids, and choline metabolites. BPH infestation caused profound metabolic changes for both BPH-susceptible and resistant rice plants involving transamination, GABA shunt, TCA cycle, gluconeogenesis/glycolysis, pentose phosphate pathway, and secondary metabolisms. BPH infestation caused more drastic overall metabolic changes for BPH-susceptible variety and more marked up-regulations for key genes regulating GABA shunt and biosynthesis of secondary metabolites for BPH-resistant variety. Such observations indicated that activation of GABA shunt and shikimate-mediated secondary metabolisms was vital for rice plants to resist BPH infestation. These findings filled the gap of our understandings in the mechanistic aspects of BPH resistance for rice plants and demonstrated the combined metabonomic and qRT-PCR analysis as an effective approach for understanding plant-herbivore interactions.

Plant β-1,3-glucanases are involved in plant defense and development. In rice (Oryza sativa), 14 genes encoding putative β-1,3-glucanases have been isolated and sequenced. However, only limited information is available on the function of these β-1,3-glucanase genes. In this study, we report a detailed functional characterization of one of these genes, Osg1. Osg1 encodes a glucanase carrying no C-terminal extension. Osg1 was found to be expressed throughout the plant and highly expressed in florets, leaf sheaths, and leaf blades. Investigations using real-time PCR, immunocytochemical analysis, and a GUS-reporter gene driven by the Osg1 promoter indicated that Osg1 was mainly expressed at the late meiosis, early microspore, and middle microspore stages in the florets. To elucidate the role of Osg1, we suppressed expression of the Osg1 gene by RNA interference in transgenic rice. The silencing of Osg1 resulted in male sterility. The pollen mother cells appeared to be normal in Osg1-RI plants, but callose degradation was disrupted around the microspores in the anther locules of the Osg1-RI plants at the early microspore stage. Consequently, the release of the young microspores into the anther locules was delayed, and the microspores began to degenerate later. These results provide evidence that Osg1 is essential for timely callose degradation in the process of tetrad dissolution.

Interspecific hybridization and polyploidization may involve programmed genetic and epigenetic changes. In this study, we used the methylation-sensitive amplified polymorphism (MSAP) method to survey cytosine methylation alterations that occurred in F(1) hybrid and BC(1) progeny following interspecific hybridization between Oryza sativa and O. officinalis. Across all 316 parental methylated sites, 25 (7.9%) cytosine methylation alterations were detected in the F(1) and/or BC(1) progeny. Thirty additional cytosine methylation alterations were detected at parental non-methylated or novel sites. In total, 55 cytosine methylation alterations (90.9% of all alterations) were detected in the F(1) hybrid, which were maintained in the BC(1) progeny. The alterations in cytosine methylation were biased toward the O. officinalis parent and were in some cases repeatable in independent hybridizations between O. sativa and O. officinalis. Twelve fragments showing cytosine methylation alterations were isolated, sequenced and subsequently validated by methylation-sensitive Southern blot analysis. Where possible, we designed species-specific primers to amplify the polymorphic transcripts from either the O. sativa or the O. officinalis parent using reverse transcription (RT)-PCR in combination with single-strand conformation polymorphism (SSCP) analysis. In four of five cases, modified gene expression could be correlated with the altered cytosine methylation pattern. Our results demonstrated cytosine methylation alterations induced by interspecific hybridization between a rice cultivar and its wild relative, and indicated a direct relationship between cytosine methylation alteration and gene expression variation.