Weilan Chen

OsELF3-1, an Ortholog of Arabidopsis EARLY FLOWERING 3, Regulates Rice Circadian Rhythm and Photoperiodic Flowering

Arabidopsis thaliana EARLY FLOWERING 3 (ELF3) as a zeitnehmer (time taker) is responsible for generation of circadian rhythm and regulation of photoperiodic flowering. There are two orthologs (OsELF3-1 and OsELF3-2) of ELF3 in rice (Oryza sativa), but their roles have not yet been fully identified. Here, we performed a functional characterization of OsELF3-1 and revealed it plays a more predominant role than OsELF3-2 in rice heading. Our results suggest OsELF3-1 can affect rice circadian systems via positive regulation of OsLHY expression and negative regulation of OsPRR1, OsPRR37, OsPRR73 and OsPRR95 expression. In addition, OsELF3-1 is involved in blue light signaling by activating EARLY HEADING DATE 1 (Ehd1) expression to promote rice flowering under short-day (SD) conditions. Moreover, OsELF3-1 suppresses a flowering repressor GRAIN NUMBER, PLANT HEIGHT AND HEADING DATE 7 (Ghd7) to indirectly accelerate flowering under long-day (LD) conditions. Taken together, our results indicate OsELF3-1 is essential for circadian regulation and photoperiodic flowering in rice.

Characterization and fine mapping of a light-dependent leaf lesion mimic mutant 1 in rice.

Plants that spontaneously produce lesion mimics or spots, without any signs of obvious adversity, such as pesticide and mechanical damage, or pathogen infection, are so-called lesion mimic mutants (lmms). In rice, many lmms exhibit enhanced resistance to pathogens, which provides a unique opportunity to uncover the molecular mechanism underlying lmms. We isolated a rice light-dependent leaf lesion mimic mutant 1 (llm1). Lesion spots appeared in the leaves of the llm1 mutant at the tillering stage. Furthermore, the mutant llm1 had similar agronomic traits to wild type rice. Trypan blue and diamiobenzidine staining analyses revealed that the lesion spot formation on the llm1 mutant was due to programmed cell death and reactive oxygen species. The chloroplasts were severely damaged in the llm1 mutant, suggesting that chloroplast damage was associated with the formation of lesion spots in llm1. More importantly, llm1 exhibited enhanced resistance to bacterial blight pathogens within increased expression of pathogenesis related genes (PRs). Using a map-based cloning approach, we delimited the LLM1 locus to a 121-kb interval between two simple sequence repeat markers, RM17470 and RM17473, on chromosome 4. We sequenced the candidate genes on the interval and found that a base mutation had substituted adenine phosphate for thymine in the last exon of LOC_Os04g52130, which led to an amino acid change (Asp(388) to Val) in the llm1 mutant. Our investigation showed that the putative coproporphyrinogen III oxidase (CPOX) encoded by LOC_Os04g52130 was produced by LLM1 and that amino acid Asp(388) was essential for CPOX function. Our study provides the basis for further investigations into the mechanism underlying lesion mimic initiation associated with LLM1.

The durably resistant rice cultivar Digu activates defence gene expression before the full maturation of Magnaporthe oryzae appressorium.

Summary Rice blast caused by the fungal pathogen M agnaporthe oryzae is one of the most destructive diseases worldwide. Although the rice–M . oryzae interaction has been studied extensively, the early molecular events that occur in rice before full maturation of the appressorium during M . oryzae invasion are unknown. Here, we report a comparative transcriptomics analysis of the durably resistant rice variety Digu and the susceptible rice variety Lijiangxintuanheigu (LTH) in response to infection by M . oryzae (5, 10 and 20 h post‐inoculation, prior to full development of the appressorium). We found that the transcriptional responses differed significantly between these two rice varieties. Gene ontology and pathway analyses revealed that many biological processes, including extracellular recognition and biosynthesis of antioxidants, terpenes and hormones, were specifically activated in Digu shortly after infection. Forty‐eight genes encoding receptor kinases (RKs) were significantly differentially regulated by M . oryzae infection in Digu. One of these genes, LOC _Os08g10300, encoding a leucine‐rich repeat RK from the LRR VIII‐2 subfamily, conferred enhanced resistance to M . oryzae when overexpressed in rice. Our study reveals that a multitude of molecular events occur in the durably resistant rice Digu before the full maturation of the appressorium after M . oryzae infection and that membrane‐associated RKs play important roles in the early response.

The Multivesicular Bodies (MVBs)-Localized AAA ATPase LRD6-6 Inhibits Immunity and Cell Death Likely through Regulating MVBs-Mediated Vesicular Trafficking in Rice

Previous studies have shown that multivesicular bodies (MVBs)/endosomes-mediated vesicular trafficking may play key roles in plant immunity and cell death. However, the molecular regulation is poorly understood in rice. Here we report the identification and characterization of a MVBs-localized AAA ATPase LRD6-6 in rice. Disruption of LRD6-6 leads to enhanced immunity and cell death in rice. The ATPase activity and homo-dimerization of LRD6-6 is essential for its regulation on plant immunity and cell death. An ATPase inactive mutation (LRD6-6E315Q) leads to dominant-negative inhibition in plants. The LRD6-6 protein co-localizes with the MVBs marker protein RabF1/ARA6 and interacts with ESCRT-III components OsSNF7 and OsVPS2. Further analysis reveals that LRD6-6 is required for MVBs-mediated vesicular trafficking and inhibits the biosynthesis of antimicrobial compounds. Collectively, our study shows that the AAA ATPase LRD6-6 inhibits plant immunity and cell death most likely through modulating MVBs-mediated vesicular trafficking in rice.

Disruption of OsEXO70A1 Causes Irregular Vascular Bundles and Perturbs Mineral Nutrient Assimilation in Rice

Normal uptake, transportation, and assimilation of primary nutrients are essential to plant growth. Tracheary elements (TEs) are tissues responsible for the transport of water and minerals and characterized by patterned secondary cell wall (SCW) thickening. Exocysts are involved in the regulation of SCW deposition by mediating the targeted transport of materials and enzymes to specific membrane areas. EXO70s are highly duplicated in plants and provide exocysts with functional specificity. In this study, we report the isolation of a rice mutant rapid leaf senescence2 (rls2) that exhibits dwarfism, ferruginous spotted necrotic leaves, decreased hydraulic transport, and disordered primary nutrient assimilation. Histological analysis of rls2-1 mutants has indicated impaired cell expansion, collapsed vascular tissues, and irregular SCW deposition. Map-based cloning has revealed that RLS2 encodes OsEXO70A1, which is one of the 47 members of EXO70s in rice. RLS2 was widely expressed and spatially restricted in vascular bundles. Subcellular localization analysis demonstrated that RLS2 was present on both membrane and nuclear regions. Expression analysis revealed that mutations in rls2 triggers transcriptional fluctuation of orthologous EXO70 genes and affects genes involved in primary nutrient absorption and transport. In brief, our study revealed that RLS2 is required for normal vascular bundle differentiation and primary nutrient assimilation.

Loss of function of a rice TPR-domain RNA-binding protein confers broad-spectrum disease resistance

Significance Crops carrying broad-spectrum resistance loci provide an effective strategy for controlling infectious disease. Despite their importance, few broad-spectrum resistance loci have been reported, and the underlying mechanisms controlling the trait remain largely unknown. This report describes the identification of a gene, called “bsr-k1,” conferring broad-spectrum resistance and demonstrates that the encoded protein regulates immunity-related genes. Loss of function of BSR-K1 in rice leads to enhanced broad-spectrum resistance to two serious rice diseases with no major penalty on yield. This report provides insights into broad-spectrum resistance and offers an efficient strategy to breeding durably resistant rice. Crops carrying broad-spectrum resistance loci provide an effective strategy for controlling infectious disease because these loci typically confer resistance to diverse races of a pathogen or even multiple species of pathogens. Despite their importance, only a few crop broad-spectrum resistance loci have been reported. Here, we report the identification and characterization of the rice bsr-k1 (broad-spectrum resistance Kitaake-1) mutant, which confers broad-spectrum resistance against Magnaporthe oryzae and Xanthomonas oryzae pv oryzae with no major penalty on key agronomic traits. Map-based cloning reveals that Bsr-k1 encodes a tetratricopeptide repeats (TPRs)-containing protein, which binds to mRNAs of multiple OsPAL (OsPAL1–7) genes and promotes their turnover. Loss of function of the Bsr-k1 gene leads to accumulation of OsPAL1–7 mRNAs in the bsr-k1 mutant. Furthermore, overexpression of OsPAL1 in wild-type rice TP309 confers resistance to M. oryzae, supporting the role of OsPAL1. Our discovery of the bsr-k1 allele constitutes a significant conceptual advancement and provides a valuable tool for breeding broad-spectrum resistant rice.

LML1, Encoding a Conserved Eukaryotic Release Factor 1 Protein, Regulates Cell Death and Pathogen Resistance by Forming a Conserved Complex with SPL33 in Rice

Lesion mimic mutants are powerful tools for unveiling the molecular connections between cell death and pathogen resistance. Various proteins responsible for lesion mimics have been identified; however, the mechanisms underlying lesion formation and pathogen resistance are still unknown. Here, we identify a lesion mimic mutant in rice, lesion mimic leaf 1 (lml1). The lml1 mutant exhibited abnormal cell death and resistance to both bacterial blight and rice blast. LML1 is expressed in all types of leaf cells, and encodes a novel eukaryotic release factor 1 (eRF1) protein located in the endoplasmic reticulum. Protein sequences of LML1 orthologs are conserved in yeast, animals and plants. LML1 can partially rescue the growth delay phenotype of the LML1 yeast ortholog mutant, dom34. Both lml1 and mutants of AtLML1 (the LML1 Arabidopsis ortholog) exhibited a growth delay phenotype like dom34. This indicates that LML1 and its orthologs are functionally conserved. LML1 forms a functional complex with a eukaryotic elongation factor 1A (eEF1A)-like protein, SPL33/LMM5.1, whose mutant phenotype was similar to the lml1 phenotype. This complex was conserved between rice and yeast. Our work provides new insight into understanding the mechanism of cell death and pathogen resistance, and also lays a good foundation for studying the fundamental molecular function of Pelota/DOM34 and its orthologs in plants.

The Receptor-Like Cytoplasmic Kinase OsRLCK102 Regulates XA21-Mediated Immunity and Plant Development in Rice

Receptor-like cytoplasmic kinases (RLCKs) belong to a large subgroup of kinases that play pivotal roles in plant development and in protecting plants from various stresses. Here, we report the isolation and characterization of rice OsRLCK102, from the OsRLCK VII subgroup. Silencing of OsRLCK102 compromised receptor kinase XA21-mediated resistance to Xanthomonas oryzae pv. oryzae (Xoo) but did not affect plant basal resistance to Xoo or Magnaporthe oryzae (M. oryzae). Plants with silenced OsRLCK102 exhibit architecture alterations, including reduced plant height, enlarged angle of the lamina joint, decreased rates of seed setting and enhanced sensitivity to hormone brassinolide (BR). Collectively, our study reveals that OsRLCK102 positively regulates XA21-mediated immunity and negatively regulates rice development through BR signaling in rice.

Characterization and fine mapping of Glabrous rice 2 in rice.

Glabrous rice exhibits glabrous leaves and hulls because neither of these structures have trichomes on their surfaces.Glabrous rice varieties have become an important germplasm resource in the rice industry because they have considerable packaging efficiency and can reduce skin itching and dust during harvesting,drying,and packing(Shim et al.,2012;Zhang et al.,2012).Trichomes are ubiquitous in land plants and they originate from the expansion of the epidermal cell and then develop through growth,differentiation,or cell division to produce hair-like tissues that extend from epidermal surfaces

08SG2 / OsBAK1 regulates grain size and number, and functions differently in Indica and Japonica backgrounds in rice

BackgroundBoth grain size and grain number are significant for rice yield. In the past decade, a number of genes related to grain size and grain number have been documented, however, the regulatory mechanisms underlying them remains ambiguous.ResultsWe identified a rice small grain (sg2) mutant in an EMS mutant library generated from an indica variety, Shuhui498. Using the MutMap gene mapping strategy, we identified two linkage regions on chromosome 7 and 8, respectively, consistent with the segregation ratios in the F2 population. We focused on the linkage region on chromosome 8, and named this locus as 08sg2. One of three SNPs identified in the linkage region was located in an exon of OsBAK1, leading to a nonsynonymous mutation in the kinase domain. The plant harboring the mutant version 08sg2 locus exhibited a decreased grain size, grain number and plant height. Cytological analysis indicated that 08SG2 regulated spikelet hull development by affecting cell proliferation. The grain size and number of knockout mutants of OsBAK1 in the japonica background were significantly decreased, but less so than in 08sg2, supporting the idea that the SNP in OsBAK1 was responsible for the 08sg2 phenotype, but that 08SG2/OsBAK1 function differently in indica and japonica backgrounds. 08sg2 was insensitive to 24-epiBL, and the expression of BR-related genes was obviously altered in 08sg2. The proportionally decreased grain length when 08sg2 and GS3 were combined indicate that 08SG2 and GS3 regulate grain length independently.ConclusionsOur work shows that 08SG2/OsBAK1 is important for rice yield in both indica and japonica backgrounds, by regulating grain size and grain number, and the function of 08SG2/OsBAK1 is obviously affected by genetic background. The amino acid substituted in 08sg2 is highly conserved among different species, supporting the idea that it is important for the molecular function of 08SG2/OsBAK1. Together, our work is helpful for fully understanding the function of 08SG2/OsBAK1.