Temporomandibular joint stress analysis of patients with different mandibular deformities during unilateral molar occlusion.

Mandibular prognathism, retrusion and deviation are common mandibular deformities. They can lead to functional and aesthetic problems due to their important role in the oral system. Different from other occlusions, unilateral molar occlusion often occurs during mastication, which has a deep impact on the functions of temporomandibular joints (TMJs). Therefore, the study of unilateral molar occlusion is of great importance and significance to the daily life of patients with mandibular deformities. A total of 35 individuals were involved in this study, including 11 asymptomatic subjects, 10 patients with mandibular prognathism, 5 patients with mandibular retrusion and 9 patients with mandibular deviation. Finite element (FE) models corresponding to the unilateral molar occlusion were constructed. During unilateral molar occlusion, mandibular deformity increases the pressure on the condyle and articular disc. Compared with mandibular protrusion or retraction, facial asymmetry will significantly increase the stress of TMJ. Chewing on the non-deviated side also will lead to higher stress in the TMJ of patients with mandibular deviation. Therefore, patients with mandibular deviation have the highest risk of temporomandibular disorder (TMD), and it is recommended that patients with mandibular deviation chew bilaterally or with the deviated side.

Uncovering key salt-tolerant regulators through a combined eQTL and GWAS analysis using the super pan-genome in rice.

For sessile plants, gene expression plays a pivotal role in responding to salinity stress by activating or suppressing specific genes. However, our knowledge of genetic variations governing gene expression in response to salt stress remains limited in natural germplasm. Through transcriptome analysis of the Global Mini-Core Rice Collection consisting of a panel of 202 accessions, we identified 22 345 and 27 610 expression quantitative trait loci associated with the expression of 7787 and 9361 eGenes under normal and salt-stress conditions, respectively, leveraging the super pan-genome map. Notably, combined with genome-wide association studies, we swiftly pinpointed the potential candidate gene STG5-a major salt-tolerant locus known as qSTS5. Intriguingly, STG5 is required for maintaining Na+/K+ homeostasis by directly regulating the transcription of multiple members of the OsHKT gene family. Our study sheds light on how genetic variants influence the dynamic changes in gene expression responding to salinity stress and provides a valuable resource for the mining of salt-tolerant genes in the future.

Moderate Salinity Stress Affects Rice Quality by Influencing Expression of Amylose- and Protein-Content-Associated Genes.

Salinity is an environmental stress that severely impacts rice grain yield and quality. However, limited information is available on the molecular mechanism by which salinity reduces grain quality. In this study, we investigated the milling, appearance, eating and cooking, and nutritional quality among three japonica rice cultivars grown either under moderate salinity with an electrical conductivity of 4 dS/m or under non-saline conditions in a paddy field in Dongying, Shandong, China. Moderate salinity affected rice appearance quality predominantly by increasing chalkiness rate and chalkiness degree and affected rice eating and cooking and nutritional quality predominantly by decreasing amylose content and increasing protein content. We compared the expression levels of genes determining grain chalkiness, amylose content, and protein content in developing seeds (0, 5, 10, 15, and 20 days after flowering) of plants grown under saline or non-saline conditions. The chalkiness-related gene Chalk5 was up-regulated and WHITE-CORE RATE 1 was repressed. The genes Nuclear factor Y and Wx, which determine amylose content, were downregulated, while protein-content-associated genes OsAAP6 and OsGluA2 were upregulated by salinity in the developing seeds. These findings suggest some target genes that may be utilized to improve the grain quality under salinity stress conditions via gene-pyramiding breeding approaches.

OsABAR1, a novel GRAM domain-containing protein, confers drought and salt tolerance via an ABA-dependent pathway in rice.

Glucosyltransferases-like GTPase activators and Myotubularin (GRAM) domain-containing proteins are important for plant development and responses to biotic stresses. However, the effects of GRAM proteins on abiotic stress responses remain unclear. In this study, we identified a novel GRAM protein-encoding gene, OsABAR1, and characterized its regulatory functions related to rice drought and salt tolerance. The OsABAR1 protein was localized in the cytoplasm and nucleus. Among all examined organs, the OsABAR1 transcript level was highest in the roots. Moreover, OsABAR1 expression was up-regulated by drought and salinity stresses. The OsABAR1-overexpressing (OsABAR1-OX) lines exhibited enhanced tolerance to drought and salinity, whereas the knock-out lines (Osabar1) had the opposite phenotypes. We further analyzed the involvement of OsABAR1 in the abscisic acid (ABA) signaling pathway. The OsABAR1 expression level was up-regulated by ABA. In turn, OsABAR1 regulated the expression of ABA metabolic genes and responsive genes. Furthermore, OsABAR1-OX seedlings were hypersensitive to exogenous ABA, whereas Osabar1 seedlings were hyposensitive. These results imply that OsABAR1 is a positive regulator of the ABA pathway and confirm that OsABAR1 improves rice drought and salt tolerance via an ABA-dependent pathway. This study is the first to clarify the regulatory roles of GRAM proteins in rice responses to abiotic stresses.

Characterization of phytochrome C functions in the control of de-etiolation and agronomic traits in rice.

Although phytochrome A (phyA) and phyB have been functionally characterized, functions of phyC in rice growth and development have remained elusive because of the functional dependency of phyC on the phyB protein. In this study, we introduced PHYB(C364A), in which the chromophore attachment site cysteine 364 was converted to alanine, into the phyAphyB double mutant (aabb) and the phyAphyBphyC triple mutant (aabbcc) to produce PHYB(C364A)/aabb lines and PHYB(C364A)/aabbcc lines, respectively. PHYB(C364A)/aabbcc lines were insensitive to red light (R) and far-red light (FR), suggesting that PHYB(C364A) protein was biologically inactive. Functions of phyC were characterized using the PHYB(C364A)/aabb lines, without the functional interference of phyA or phyB. Phytochrome C responded to R and FR to trigger de-etiolation in the very-low-fluence response and low-fluence response in the PHYB(C364A)/aabb lines. Compared with the aabb mutant, seedlings of PHYB(C364A)/aabb lines showed higher chlorophyll content and reduced leaf angle. The PHYB(C364A)/aabb lines also showed a delayed heading date under long-day conditions. Phytochrome C-regulated agronomic traits were measured at the mature stage. The PHYB(C364A)/aabb lines showed significantly increased plant height, panicle length, grain number per main panicle, seed-setting rate, grain size, and grain weight, compared with those of the aabb mutant. Taken together, the present findings confirm that phyC perceives R and FR, and plays an important role in photomorphogenesis and yield determination in rice.

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.

Phytochrome B Negatively Affects Cold Tolerance by Regulating OsDREB1 Gene Expression through Phytochrome Interacting Factor-Like Protein OsPIL16 in Rice.

Cross talk between light signaling and cold signaling has been elucidated in the model plant Arabidopsis and tomato, but little is known about their relationship in rice. Here, we report that phytochrome B (phyB) mutants exhibit improved cold tolerance compared with wild type (WT) rice (Oryza sativa L. cv. Nipponbare). The phyB mutants had a lower electrolyte leakage index and malondialdehyde concentration than the WT, suggesting that they had greater cell membrane integrity and less lipid peroxidation. Real-time PCR analysis revealed that the expression levels of dehydration-responsive element binding protein 1 (OsDREB1) family genes, which functions in the cold stress response in rice, were increased in the phyB mutant under normal and cold stress conditions. PIFs are central players in phytochrome-mediated light signaling networks. To explore the relationship between rice PIFs and OsDREB1 gene expression, we produced overexpression lines of rice PIF genes. OsDREB1 family genes were up-regulated in OsPIL16-overexpression lines, which had improved cold tolerance relative to the WT. Chromatin immunoprecipitation (ChIP)-qPCR assay revealed that OsPIL16 can bind to the N-box region of OsDREB1B promoter. Expression pattern analyses revealed that OsPIL16 transcripts were induced by cold stress and was significantly higher in the phyB mutant than in the WT. Moreover, yeast two-hybrid assay showed that OsPIL16 can bind to rice PHYB. Based on these results, we propose that phyB deficiency positively regulates OsDREB1 expression through OsPIL16 to enhance cell membrane integrity and to reduce the malondialdehyde concentration, resulting in the improved cold tolerance of the phyB mutants.

XA23 is an executor R protein and confers broad-spectrum disease resistance in rice.

The majority of plant disease resistance (R) genes encode proteins that share common structural features. However, the transcription activator-like effector (TALE)-associated executor type R genes show no considerable sequence homology to any known R genes. We adopted a map-based cloning approach and TALE-based technology to isolate and characterize Xa23, a new executor R gene derived from wild rice (Oryza rufipogon) that confers an extremely broad spectrum of resistance to bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo). Xa23 encodes a 113 amino acid protein that shares 50% identity with the known executor R protein XA10. The predicted transmembrane helices in XA23 also overlap with those of XA10. Unlike Xa10, however, Xa23 transcription is specifically activated by AvrXa23, a TALE present in all examined Xoo field isolates. Moreover, the susceptible xa23 allele has an identical open reading frame of Xa23 but differs in promoter region by lacking the TALE binding element (EBE) for AvrXa23. XA23 can trigger a strong hypersensitive response in rice, tobacco, and tomato. Our results provide the first evidence that plant genomes have an executor R gene family of which members execute their function and spectrum of disease resistance by recognizing the cognate TALEs in the pathogen.

XA23 is an executor R protein and confers broad-spectrum disease resistance in rice.

The majority of plant disease resistance (R) genes encode proteins that share common structural features. However, the transcription activator-like effector (TALE) associated executor type R genes show no considerable sequence homology to any known R genes. We adopted a map-based cloning approach and TALE-based technology to isolate and characterize Xa23, a new executor R gene derived from the wild rice (Oryza rufipogon) that confers an extremely broad spectrum of resistance to bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo). Xa23 encodes a 113-amino acid protein that shares 50% identity to the known executor R protein XA10. The predicted transmembrane helices in XA23 also overlap with those of XA10. Unlike Xa10, however, Xa23 transcription is specifically activated by AvrXa23, a TALE present in all examined Xoo field isolates. Moreover, the susceptible xa23 allele has an identical open reading frame of Xa23, but differs in promoter region by lacking the TALE binding-element (EBE) for AvrXa23. XA23 can trigger strong hypersensitive response in rice, tobacco and tomato. Our results provide the first evidence that plant genomes have an executor R gene family in which members execute their function and spectrum of disease resistance by recognizing the cognate TALEs in pathogen.

High-resolution genetic mapping of rice bacterial blight resistance gene Xa23.

Bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is the most devastating bacterial disease of rice (Oryza sativa L.), a staple food crop that feeds half of the world's population. In management of this disease, the most economical and effective approach is cultivating resistant varieties. Due to rapid change of pathogenicity in the pathogen, it is necessary to identify and characterize more host resistance genes for breeding new resistant varieties. We have previously identified the BB resistance (R) gene Xa23 that confers the broadest resistance to Xoo strains isolated from different rice-growing regions and preliminarily mapped the gene within a 1.7 cm region on the long arm of rice chromosome 11. Here, we report fine genetic mapping and in silico analysis of putative candidate genes of Xa23. Based on F2 mapping populations derived from crosses between Xa23-containing rice line CBB23 and susceptible varieties JG30 or IR24, six new STS markers Lj36, Lj46, Lj138, Lj74, A83B4, and Lj13 were developed. Linkage analysis revealed that the new markers were co-segregated with or closely linked to the Xa23 locus. Consequently, the Xa23 gene was mapped within a 0.4 cm region between markers Lj138 and A83B4, in which the co-segregating marker Lj74 was identified. The corresponding physical distance between Lj138 and A83B4 on Nipponbare genome is 49.8 kb. Six Xa23 candidate genes have been annotated, including four candidate genes encoding hypothetical proteins and the other two encoding a putative ADP-ribosylation factor protein and a putative PPR protein. These results will facilitate marker-assisted selection of Xa23 in rice breeding and molecular cloning of this valuable R gene.

The last half-repeat of transcription activator-like effector (TALE) is dispensable and thereby TALE-based technology can be simplified.

To activate the expression of host genes that contribute to pathogen growth, pathogenic Xanthomonas bacteria inject their transcription activator-like effectors (TALEs) into plant cells and the TALEs bind to target gene promoters by the central repeat region consisting of near-perfect 34-amino-acid repeats (34-aa repeats). Based on the recognition codes between the 34-aa repeats and the targeted nucleotides, TALE-based technologies, such as designer TALEs (dTALEs) and TALE nucleases (TALENs), have been developed. Amazingly, every natural TALE invariantly has a truncated last half-repeat (LHR) at the end of the 34-aa repeats. Consequently, all the reported dTALEs and TALENs also harbour their LHRs. Here, we show that the LHRs in dTALEs are dispensable for the function of gene activation by both transient expression assays in Nicotiana benthamiana and gene-specific targeting in the rice genome, indicating that TALEs might originate from a single progenitor. In the light of this finding, we demonstrate that dTALEs can be constructed through two simple steps. Moreover, the activation strengths of dTALEs lacking the LHR are comparable with those of dTALEs harbouring the LHR. Our results provide new insights into the origin of natural TALEs, and will facilitate the simplification of the design and assembly of TALE-based tools, such as dTALEs and TALENs, in the near future.

The broad bacterial blight resistance of rice line CBB23 is triggered by a novel transcription activator-like (TAL) effector of Xanthomonas oryzae pv. oryzae.

Bacterial blight (BB), caused by Xanthomonas oryzae pv. oryzae (Xoo), is not only a disease devastating rice production worldwide, but also an ideal model system for the study of the interaction between plants and their bacterial pathogens. The rice near-isogenic line (NIL) CBB23, derived from a cross between a wild rice Oryza rufipogon accession (RBB16) and a susceptible indica rice variety (Jingang 30), is highly resistant to all field Xoo strains tested so far. Although the BB resistance of CBB23 has been widely used in rice breeding programmes, the mechanism of its extremely broad-spectrum resistance remains unknown. Here, we report the molecular cloning of an avirulence gene, designated as avrXa23, from Xoo strain PXO99(A) . We validate that AvrXa23, a novel transcription activator-like effector, specifically triggers the broad-spectrum BB resistance in CBB23. The prevalence of avrXa23 in all 38 Xoo strains surveyed may explain the broad-spectrum feature of BB resistance in CBB23. The results will significantly facilitate the molecular cloning of the corresponding resistance (R) gene in the host, and provide new insights into our understanding of the molecular mechanism for broad-spectrum disease resistance in plants.