Phytochrome B mediates dim-light-reduced insect resistance by promoting the ethylene pathway in rice.

Increasing planting density is one of the most effective ways to improve crop yield. However, one major factor that limits crop planting density is the weakened immunity of plants to pathogens and insects caused by dim light (DL) under shade conditions. The molecular mechanism underlying how DL compromises plant immunity remains unclear. Here, we report that DL reduces rice (Oryza sativa) resistance against brown planthopper (BPH; Nilaparvata lugens) by elevating ethylene (ET) biosynthesis and signaling in a Phytochrome B (OsPHYB)-dependent manner. The DL-reduced BPH resistance is relieved in osphyB mutants, but aggravated in OsPHYB overexpressing plants. Further, we found that DL reduces the nuclear accumulation of OsphyB, thus alleviating Phytochrome Interacting Factor Like14 (OsPIL14) degradation, consequently leading to the up-regulation of 1-Aminocyclopropane-1-Carboxylate Oxidase1 (OsACO1) and an increase in ET levels. In addition, we found that nuclear OsphyB stabilizes Ethylene Insensitive Like2 (OsEIL2) by competitively interacting with EIN3 Binding F-Box Protein (OsEBF1) to enhance ET signaling in rice, which contrasts with previous findings that phyB blocks ET signaling by facilitating Ethylene Insensitive3 (EIN3) degradation in other plant species. Thus, enhanced ET biosynthesis and signaling reduces BPH resistance under DL conditions. Our findings provide insights into the molecular mechanism of the light-regulated ET pathway and host-insect interactions and potential strategies for sustainable insect management.

The Rice Phytochrome Genes, PHYA and PHYB, Have Synergistic Effects on Anther Development and Pollen Viability.

Phytochromes are the main plant photoreceptors regulating multiple developmental processes. However, the regulatory network of phytochrome-mediated plant reproduction has remained largely unexplored. There are three phytochromes in rice, phyA, phyB and phyC. No changes in fertility are observed in the single mutants, whereas the seed-setting rate of the phyA phyB double mutant is significantly reduced. Histological and cytological analyses showed that the reduced fertility of the phyA phyB mutant was due to defects in both anther and pollen development. The four anther lobes in the phyA phyB mutant were developed at different stages with fewer pollen grains, most of which were aborted. At the mature stage, more than one lobe in the double mutant was just consisted of several cell layers. To identify genes involved in phytochrome-mediated anther development, anther transcriptomes of phyA, phyB and phyA phyB mutants were compared to that of wild-type rice respectively. Analysis of 2,241 double-mutant-specific differentially expressed transcripts revealed that the metabolic profiles, especially carbohydrate metabolism, were altered greatly, and heat-shock responses were activated in the double mutant. This study firstly provides valuable insight into the complex regulatory networks underlying phytochrome-mediated anther and pollen development in plants, and offers novel clues for hybrid rice breeding.

Deficiency of phytochrome B alleviates chilling-induced photoinhibition in rice.

PREMISE OF THE STUDY: Food crops of tropical origins, such as rice, are often cultivated in areas with suboptimal temperature regimes. The rice phytochrome B-deficient mutant (phyB) is tolerant of chilling temperatures compared with the wild type (WT) under low irradiance, and unsaturated fatty acids (USFAs) of membrane lipids have been shown to play an important role in chilling resistance. However, the relationship between phytochrome B and membrane lipids has not been empirically investigated. • METHODS: We assessed various photosynthesis indexes in phyB and WT rice: chlorophyll content, maximal photochemical efficiency (Fv/Fm) of photosystem II (PSII), the quantum yield of PSII electron transport (ΦPSII), the percentage of oxidizable P700 (P700), nonphotochemical quenching (NPQ), and the de-epoxidized ratio of xanthophyll cycle (A+Z)/(V+A+Z). We also analyzed the ultrastructure and fatty acid desaturases (FADs) and glycerol-3-phosphate acyltransferase (GPAT) genes of the chloroplasts using transmission electron microscopy and real-time PCR. • RESULTS: After a chilling treatment of 24 h, chloroplast damage and USFA content reduction were more severe in the WT than in the phyB mutant. Genes involved in the synthesis of USFAs in membranes such as FADs and GPAT were more stable in phyB than in WT. Chlorophyll content, Fv/Fm, ΦPSII, and P700 decreased more slowly under chilling stress and recovered more rapidly under optimal conditions in phyB than in WT. The (A+Z)/(V+A+Z) and NPQ increased more rapidly in phyB than in the WT after 24 h of chilling treatment. • CONCLUSIONS: Phytochrome B deficiency in rice with more stabilized chloroplast structure and higher USFA content in membrane lipids could alleviate chilling-induced photoinhibition.

[Regulation of stomatal development in plants].

Stomata mediate gas exchanges between plant and environment. To adapt to environmental conditions, plants open and close stomatal pores and even regulate the number of stomata that develop on the epidermis. Recent studies have brought to light the elements of the genetic basis underlying stomatal development. They have also revealed how these elements are controlled by environmental factors (mainly light and carbon dioxide). In this review, we discussed the molecular basis of stomatal development and physiological mechanisms regulating this process. Future prospects related to stomatal development are proposed.

Phytochromes regulate SA and JA signaling pathways in rice and are required for developmentally controlled resistance to Magnaporthe grisea.

Old leaves of wild-type rice plants (Oryza sativa L. cv. Nipponbare) are more resistant to blast fungus (Magnaporthe grisea) than new leaves. In contrast, both old and new leaves of the rice phytochrome triple mutant (phyAphyBphyC) are susceptible to blast fungus. We demonstrate that pathogenesis-related class 1 (PR1) proteins are rapidly and strongly induced during M. grisea infection and following exogenous jasmonate (JA) or salicylic acid (SA) exposure in the old leaves, but not in the new leaves of the wild-type. In contrast, the accumulation of PR1 proteins was significantly attenuated in old and new leaves of the phyAphyBphyC mutant. These results suggest that phytochromes are required for the induction of PR1 proteins in rice. Basal transcription levels of PR1a and PR1b were substantially higher in the wild-type as compared to the phyAphyBphyC mutant, suggesting that phytochromes also are required for basal expression of PR1 genes. Moreover, the transcript levels of genes known to function in SA- or JA-dependent defense pathways were regulated by leaf age and functional phytochromes. Taken together, our findings demonstrate that phytochromes are required in rice for age-related resistance to M. grisea and may indirectly increase PR1 gene expression by regulating SA- and JA-dependent defense pathways.

Isolation and functional assessment of a tomato proteinase inhibitor II gene.

A genomic clone encoding a serine proteinase inhibitor II, designated as TPI-2, was isolated from tomato (Lycopersicon esculentum Mill.) seedling. It consisted of a 990 bp upstream regulatory region and a 680 bp transcription region containing an intron. As shown by northern hybridization, mechanical injury activated its expression in roots, stems and leaves, and so did exogenous hormones jasmonic acid (JA) and alpha-Linolenic acid (LA), though abscisic acid (ABA) and NaCl failed to induce its expression. Salicylic acid (SA) was found to inhibit the inducing effect of LA but not those of mechanical injury and JA. As demonstrated experimentally, TPI-2 could be expressed effectively in tobacco cells and the protein products showed insecticidal activity.