4-Coumarate:coenzyme A ligase (4CL; EC 6.2.1.12) is a key enzyme in the phenylpropanoid metabolic pathways for monolignol and flavonoid biosynthesis. 4CL has been much studied in dicotyledons, but its function is not completely understood in monocotyledons, which display a different monolignol composition and phenylpropanoid profile. In this study, five members of the 4CL gene family in the rice (Oryza sativa) genome were cloned and analyzed. Biochemical characterization of the 4CL recombinant proteins revealed that the rice 4CL isoforms displayed different substrate specificities and catalytic turnover rates. Among them, Os4CL3 exhibited the highest turnover rate. No apparent tissue-specific expression of the five 4CLs was observed, but significant differences in their expression levels were detected. The rank in order of transcript abundance was Os4CL3 . Os4CL5 . Os4CL1 . Os4CL4 . Os4CL2. Suppression of Os4CL3 expression resulted in significant lignin reduction, shorter plant growth, and other morphological changes. The 4CL-suppressed transgenics also displayed decreased panicle fertility, which may be attributed to abnormal anther development as a result of disrupted lignin synthesis. This study demonstrates that the rice 4CLs exhibit different in vitro catalytic properties from those in dicots and that 4CL-mediated metabolism in vivo may play important roles in regulating a broad range of biological events over the course of rice growth and development.

Salt stress can significantly affect plant growth and agricultural productivity. Receptor-like kinases (RLKs) are believed to play essential roles in plant growth, development, and responses to abiotic stresses. Here, we identify a receptor-like cytoplasmic kinase, salt tolerance receptor-like cytoplasmic kinase 1 (STRK1), from rice () that positively regulates salt and oxidative stress tolerance. Our results show that STRK1 anchors and interacts with CatC at the plasma membrane via palmitoylation. CatC is phosphorylated mainly at Tyr-210 and is activated by STRK1. The phosphorylation mimic form CatC exhibits higher catalase activity both in vitro and in planta, and salt stress enhances STRK1-mediated tyrosine phosphorylation on CatC. Compared with wild-type plants, -overexpressing plants exhibited higher catalase activity and lower accumulation of HO as well as higher tolerance to salt and oxidative stress. Our findings demonstrate that STRK1 improves salt and oxidative tolerance by phosphorylating and activating CatC and thereby regulating HO homeostasis. Moreover, overexpression of in rice not only improved growth at the seedling stage but also markedly limited the grain yield loss under salt stress conditions. Together, these results offer an opportunity to improve rice grain yield under salt stress.

Crosstalk among phytohormones is crucial for balancing plant growth and adjustment to various environments. Abscisic acid (ABA) and brassinosteroids (BRs) exhibit antagonistic interactions during many plant development processes, but little is known about the molecular mechanism mediating those interactions. Here, we identified a rice (Oryza sativa) remorin gene, OsREM4.1, whose expression is upregulated by ABA through the transcriptional activator OsbZIP23. OsREM4.1, in return, negatively regulates BR signaling output. We discovered that OsREM4.1 interacts with OsSERK1 to inhibit its interaction with rice BR receptor OsBRI1. Moreover, OsBRI1 could phosphorylate OsREM4.1 to reduce the binding affinity of OsREM4.1 to OsSERK1. These results demonstrate that OsREM4.1 is transcriptionally regulated by ABA and functions as an OsBRI1 substrate and OsSERK1-interacting protein to inhibit the formation and subsequent activation of the OsBRI1-OsSERK1 receptor complex. Our findings provide insight into the mechanism by which the antagonistic interactions between ABA and BRs are coordinated in rice.

Effective grain filling is one of the key determinants of grain setting in rice (Oryza sativa). Grain setting defect1 (GSD1), which encodes a putative remorin protein, was found to affect grain setting in rice. Investigation of the phenotype of a transfer DNA insertion mutant (gsd1-Dominant) with enhanced GSD1 expression revealed abnormalities including a reduced grain setting rate, accumulation of carbohydrates in leaves, and lower soluble sugar content in the phloem exudates. GSD1 was found to be specifically expressed in the plasma membrane and plasmodesmata (PD) of phloem companion cells. Experimental evidence suggests that the phenotype of the gsd1-Dominant mutant is caused by defects in the grain-filling process as a result of the impaired transport of carbohydrates from the photosynthetic site to the phloem. GSD1 functioned in affecting PD conductance by interacting with rice ACTIN1 in association with the PD callose binding protein1. Together, our results suggest that GSD1 may play a role in regulating photoassimilate translocation through the symplastic pathway to impact grain setting in rice.

Breeding semi-dwarf varieties to improve lodging resistance has been proven to be enormously successful in increasing grain yield since the advent of the "green revolution." However, the breeding of the majority of semi-dwarf rice varieties in Asia has been dependent mainly on genetic introduction of the mutant alleles of SD1, which encodes a gibberellin (GA) 20-oxidase, OsGA20ox2, for catalyzing GA biosynthesis. Here, we report a new rice lodging-resistance gene, Shortened Basal Internodes (SBI), which encodes a gibberellin 2-oxidase and specifically controls the elongation of culm basal internodes through deactivating GA activity. SBI is predominantly expressed in culm basal internodes. Genetic analyses indicate that SBI is a semi-dominant gene affecting rice height and lodging resistance. SBI allelic variants display different activities and are associated with the height of rice varieties. Breeding with higher activity of the SBI allele generates new rice varieties with improved lodging resistance and increased yield. The discovery of the SBI provides a desirable gene resource for producing semi-dwarf rice phenotypes and offers an effective strategy for breeding rice varieties with enhanced lodging resistance and high yield.

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Lignin is a major component of cell wall biomass and decisively affects biomass utilisation. Engineering of lignin biosynthesis is extensively studied, while lignin modification often causes growth defects.We developed a strategy for cell-type-specific modification of lignin to achieve improvements in cell wall property without growth penalty. We targeted a lignin-related transcription factor, LTF1, for modification of lignin biosynthesis. LTF1 can be engineered to a nonphosphorylation form which is introduced into Populus under the control of either a vessel-specific or fibre-specific promoter.The transgenics with lignin suppression in vessels showed severe dwarfism and thin-walled vessels, while the transgenics with lignin suppression in fibres displayed vigorous growth with normal vessels under phytotron, glasshouse and field conditions. In-depth lignin structural analyses revealed that such cell-type-specific downregulation of lignin biosynthesis led to the alteration of overall lignin composition in xylem tissues reflecting the population of distinctive lignin polymers produced in vessel and fibre cells.This study demonstrates that fibre-specific suppression of lignin biosynthesis resulted in the improvement of wood biomass quality and saccharification efficiency and presents an effective strategy to precisely regulate lignin biosynthesis with desired growth performance.