Dysfunction of duplicated pair rice histone acetyltransferases causes segregation distortion and an interspecific reproductive barrier

Postzygotic reproductive isolation, which results in the irreversible divergence of species, is commonly accompanied by hybrid sterility, necrosis/weakness, or lethality in the F1 or other offspring generations. Here we show that the loss of function of HWS1 and HWS2, a couple of duplicated paralogs, together confer complete interspecific incompatibility between Asian and African rice. Both of these non-Mendelian determinants encode the putative Esa1-associated factor 6 (EAF6) protein, which functions as a characteristic subunit of the histone H4 acetyltransferase complex regulating transcriptional activation via genome-wide histone modification. The proliferating tapetum and inappropriate polar nuclei arrangement cause defective pollen and seeds in F2 hybrid offspring due to the recombinant HWS1/2-mediated misregulation of vitamin (biotin and thiamine) metabolism and lipid synthesis. Evolutionary analysis of HWS1/2 suggests that this gene pair has undergone incomplete lineage sorting (ILS) and multiple gene duplication events during speciation. Our findings have not only uncovered a pair of speciation genes that control hybrid breakdown but also illustrate a passive mechanism that could be scaled up and used in the guidance and optimization of hybrid breeding applications for distant hybridization.

Optimization of rice panicle architecture by specifically suppressing ligand-receptor pairs

Rice panicle architecture determines the grain number per panicle and therefore impacts grain yield. The OsER1-OsMKKK10-OsMKK4-OsMPK6 pathway shapes panicle architecture by regulating cytokinin metabolism. However, the specific upstream ligands perceived by the OsER1 receptor are unknown. Here, we report that the EPIDERMAL PATTERNING FACTOR (EPF)/EPF-LIKE (EPFL) small secreted peptide family members OsEPFL6, OsEPFL7, OsEPFL8, and OsEPFL9 synergistically contribute to rice panicle morphogenesis by recognizing the OsER1 receptor and activating the mitogen-activated protein kinase cascade. Notably, OsEPFL6, OsEPFL7, OsEPFL8, and OsEPFL9 negatively regulate spikelet number per panicle, but OsEPFL8 also controls rice spikelet fertility. A osepfl6 osepfl7 osepfl9 triple mutant had significantly enhanced grain yield without affecting spikelet fertility, suggesting that specifically suppressing the OsEPFL6-OsER1, OsEPFL7-OsER1, and OsEPFL9-OsER1 ligand-receptor pairs can optimize rice panicle architecture. These findings provide a framework for fundamental understanding of the role of ligand-receptor signaling in rice panicle development and demonstrate a potential method to overcome the trade-off between spikelet number and fertility.

An α/β hydrolase family member negatively regulates salt tolerance but promotes flowering through three distinct functions in rice

Ongoing soil salinization drastically threatens crop growth, development, and yield worldwide. It is therefore crucial that we improve salt tolerance in rice by exploiting natural genetic variation. However, many salt-responsive genes confer undesirable phenotypes and therefore cannot be effectively applied to practical agricultural production. In this study, we identified a quantitative trait locus for salt tolerance from the African rice species Oryza glaberrima and named it as Salt Tolerance and Heading Date 1 (STH1). We found that STH1 regulates fatty acid metabolic homeostasis, probably by catalyzing the hydrolytic degradation of fatty acids, which contributes to salt tolerance. Meanwhile, we demonstrated that STH1 forms a protein complex with D3 and a vital regulatory factor in salt tolerance, OsHAL3, to regulate the protein abundance of OsHAL3 via the 26S proteasome pathway. Furthermore, we revealed that STH1 also serves as a co-activator with the floral integrator gene Heading date 1 to balance the expression of the florigen gene Heading date 3a under different circumstances, thus coordinating the regulation of salt tolerance and heading date. Notably, the allele of STH1 associated with enhanced salt tolerance and high yield is found in some African rice accessions but barely in Asian cultivars. Introgression of the STH1^HP46 allele from African rice into modern rice cultivars is a desirable approach for boosting grain yield under salt stress. Collectively, our discoveries not only provide conceptual advances on the mechanisms of salt tolerance and synergetic regulation between salt tolerance and flowering time but also offer potential strategies to overcome the challenges resulted from increasingly serious soil salinization that many crops are facing.

A genetic module at one locus in rice protects chloroplasts to enhance thermotolerance

How the plasma membrane senses external heat-stress signals to communicate with chloroplasts to orchestrate thermotolerance remains elusive. We identified a quantitative trait locus, Thermo-tolerance 3 (TT3), consisting of two genes, TT3.1 and TT3.2, that interact together to enhance rice thermotolerance and reduce grain-yield losses caused by heat stress. Upon heat stress, plasma membrane-localized E3 ligase TT3.1 translocates to the endosomes, on which TT3.1 ubiquitinates chloroplast precursor protein TT3.2 for vacuolar degradation, implying that TT3.1 might serve as a potential thermosensor. Lesser accumulated, mature TT3.2 proteins in chloroplasts are essential for protecting thylakoids from heat stress. Our findings not only reveal a TT3.1-TT3.2 genetic module at one locus that transduces heat signals from plasma membrane to chloroplasts but also provide the strategy for breeding highly thermotolerant crops.

TT2 controls rice thermotolerance through SCT1-dependent alteration of wax biosynthesis

Global warming threatens crop production. G proteins mediate plant responses to multiple abiotic stresses. Here we identified a natural quantitative trait locus, TT2 (THEROMOTOLERANCE 2), encoding a Gγ subunit, that confers thermotolerance in rice during both vegetative and reproductive growth without a yield penalty. A natural allele with loss of TT2 function was associated with greater retention of wax at high temperatures and increased thermotolerance. Mechanistically, we found that a transcription factor, SCT1 (Sensing Ca²⁺ Transcription factor 1), functions to decode Ca²⁺ through Ca²⁺-enhanced interaction with calmodulin and acts as a negative regulator of its target genes (for example, Wax Synthesis Regulatory 2 (OsWR2)). The calmodulin-SCT1 interaction was attenuated by reduced heat-triggered Ca²⁺ caused by disrupted TT2, thus explaining the observed heat-induced changes in wax content. Beyond establishing a bridge linking G protein, Ca²⁺ sensing and wax metabolism, our study illustrates innovative approaches for developing potentially yield-penalty-free thermotolerant crop varieties.

ERECTA1 Acts Upstream of the OsMKKK10-OsMKK4-OsMPK6 Cascade to Control Spikelet Number by Regulating Cytokinin Metabolism in Rice

Grain number is a flexible trait that strongly contributes to grain yield. In rice (Oryza sativa), the OsMKKK10-OsMKK4-OsMPK6 cascade, which is negatively regulated by the dual-specificity phosphatase GSN1, coordinates the trade-off between grain number and grain size. However, the specific components upstream and downstream of the GSN1-MAPK module that regulate spikelet number per panicle remain obscure. Here, we report that ERECTA1 (OsER1), a negative regulator of spikelet number per panicle, acts upstream of the OsMKKK10-OsMKK4-OsMPK6 cascade and that the OsER1-OsMKKK10-OsMKK4-OsMPK6 pathway is required to maintain cytokinin homeostasis. OsMPK6 directly interacts with and phosphorylates the zinc finger transcription factor DST to enhance its transcriptional activation of CYTOKININ OXIDASE2 (OsCKX2), indicating that the OsER1-OsMKKK10-OsMKK4-OsMPK6 pathway shapes panicle morphology by regulating cytokinin metabolism. Furthermore, overexpression of either DST or OsCKX2 rescued the spikelet number phenotype of the oser1, osmkkk10, osmkk4, and osmpk6 mutants, suggesting that the DST-OsCKX2 module genetically functions downstream of the OsER1-OsMKKK10-OsMKK4-OsMPK6 pathway. These findings reveal specific crosstalk between a MAPK signaling pathway and cytokinin metabolism, shedding light on how developmental signals modulate phytohormone homeostasis to shape the inflorescence.

A quantitative trait locus GW6 controls rice grain size and yield through the gibberellin pathway

Grain size is one of the essential components determining rice yield and is a target for both domestication and artificial breeding. Gibberellins (GAs) are diterpenoid phytohormones that influence diverse aspects of plant growth and development. Several quantitative trait loci (QTLs) have been identified that control grain size through phytohormone regulation. However, little is known about the role of GAs in the control of grain size. Here we report the cloning and characterization of a QTL, GW6 (GRAIN WIDTH 6), which encodes a GA-regulated GAST family protein and positively regulates grain width and weight. GW6 is highly expressed in the young panicle and increases grain width by promoting cell expansion in the spikelet hull. Knockout of GW6 exhibits reduced grain size and weight, whereas overexpression of GW6 results in increased grain size and weight. GW6 is induced by GA and its knockout downregulates the expression of GA biosynthesis genes and decreases GA content in the young panicle. We found that a natural variation in the cis element CAAT-box in the promoter of GW6 is associated with its expression level and grain width and weight. Furthermore, introduction of GW6 to Oryza indica variety HJX74 can lead to a 10.44% increase in rice grain yield, indicating that GW6 has great potential to improve grain yield in rice.

Tillering and small grain 1 dominates the tryptophan aminotransferase family required for local auxin biosynthesis in rice

Auxin is a crucial phytohormone, controlling multiple aspects of plant growth and responses to the changing environment. However, the role of local auxin biosynthesis in specific developmental programs remains unknown in crops. This study characterized the rice tillering and small grain 1 (tsg1) mutant, which has more tillers but a smaller panicle and grain size resulting from a reduction in endogenous auxin. TSG1 encodes a tryptophan aminotransferase that is allelic to the FISH BONE (FIB) gene. The tsg1 mutant showed hypersensitivity to indole-3-acetic acid and the competitive inhibitor of aminotransferase, L-kynurenine. TSG1 knockout resulted in an increased tiller number but reduction in grain number and size, and decrease in height. Meanwhile, deletion of the TSG1 homologs OsTAR1, OsTARL1, and OsTARL2 caused no obvious changes, although the phenotype of the TSG1/OsTAR1 double mutant was intensified and infertile, suggesting gene redundancy in the rice tryptophan aminotransferase family. Interestingly, TSG1 and OsTAR1, but not OsTARL1 and OsTARL2, displayed marked aminotransferase activity. Meanwhile, subcellular localization was identified as the endoplasmic reticulum, while phylogenetic analysis revealed functional divergence of TSG1 and OsTAR1 from OsTARL1 and OsTARL2. These findings suggest that TSG1 dominates the tryptophan aminotransferase family, playing a prominent role in local auxin biosynthesis in rice.

A SAC Phosphoinositide Phosphatase Controls Rice Development via Hydrolyzing PI4P and PI(4,5)P2

Phosphoinositides (PIs) as regulatory membrane lipids play essential roles in multiple cellular processes. Although the exact molecular targets of PI-dependent modulation remain largely elusive, the effects of disturbed PI metabolism could be employed to identify regulatory modules associated with particular downstream targets of PIs. Here, we identified the role of GRAIN NUMBER AND PLANT HEIGHT1 (GH1), which encodes a suppressor of actin (SAC) domain-containing phosphatase with unknown function in rice (Oryza sativa). Endoplasmic reticulum-localized GH1 specifically dephosphorylated and hydrolyzed phosphatidylinositol 4-phosphate (PI4P) and phosphatidylinositol 4,5-bisphosphate [PI(4,5)P₂]. Inactivation of GH1 resulted in massive accumulation of both PI4P and PI(4,5)P₂, while excessive GH1 caused their depletion. Notably, superabundant PI4P and PI(4,5)P₂ could both disrupt actin cytoskeleton organization and suppress cell elongation. Interestingly, both PI4P and PI(4,5)P₂ inhibited actin-related protein2 and -3 (Arp2/3) complex-nucleated actin-branching networks in vitro, whereas PI(4,5)P₂ showed more dramatic effects in a dose-dependent manner. Overall, the overaccumulation of PI(4,5)P₂ resulting from dysfunction of SAC phosphatase possibly perturbs Arp2/3 complex-mediated actin polymerization, thereby disordering cell development. These findings imply that the Arp2/3 complex might be the potential molecular target of PI(4,5)P₂-dependent modulation in eukaryotes, thereby providing insights into the relationship between PI homeostasis and plant growth and development.

NAL8 encodes a prohibitin that contributes to leaf and spikelet development by regulating mitochondria and chloroplasts stability in rice

BACKGROUND

Leaf morphology and spikelet number are two important traits associated with grain yield. To understand how genes coordinating with sink and sources of cereal crops is important for grain yield improvement guidance. Although many researches focus on leaf morphology or grain number in rice, the regulating molecular mechanisms are still unclear.

RESULTS

In this study, we identified a prohibitin complex 2α subunit, NAL8, that contributes to multiple developmental process and is required for normal leaf width and spikelet number at the reproductive stage in rice. These results were consistent with the ubiquitous expression pattern of NAL8 gene. We used genetic complementation, CRISPR/Cas9 gene editing system, RNAi gene silenced system and overexpressing system to generate transgenic plants for confirming the fuctions of NAL8. Mutation of NAL8 causes a reduction in the number of plastoglobules and shrunken thylakoids in chloroplasts, resulting in reduced cell division. In addition, the auxin levels in nal8 mutants are higher than in TQ, while the cytokinin levels are lower than in TQ. Moreover, RNA-sequencing and proteomics analysis shows that NAL8 is involved in multiple hormone signaling pathways as well as photosynthesis in chloroplasts and respiration in mitochondria.

CONCLUSIONS

Our findings provide new insights into the way that NAL8 functions as a molecular chaperone in regulating plant leaf morphology and spikelet number through its effects on mitochondria and chloroplasts associated with cell division.

Translational Regulation of Plant Response to High Temperature by a Dual-Function tRNAHis Guanylyltransferase in Rice

As sessile organisms, plants have evolved numerous strategies to acclimate to changes in environmental temperature. However, the molecular basis of this acclimation remains largely unclear. In this study we identified a tRNA^His guanylyltransferase, AET1, which contributes to the modification of pre-tRNA^His and is required for normal growth under high-temperature conditions in rice. Interestingly, AET1 possibly interacts with both RACK1A and eIF3h in the endoplasmic reticulum. Notably, AET1 can directly bind to OsARF mRNAs including the uORFs of OsARF19 and OsARF23, indicating that AET1 is associated with translation regulation. Furthermore, polysome profiling assays suggest that the translational status remains unaffected in the aet1 mutant, but that the translational efficiency of OsARF19 and OsARF23 is reduced; moreover, OsARF23 protein levels are obviously decreased in the aet1 mutant under high temperature, implying that AET1 regulates auxin signaling in response to high temperature. Our findings provide new insights into the molecular mechanisms whereby AET1 regulates the environmental temperature response in rice by playing a dual role in tRNA modification and translational control.

GRAIN SIZE AND NUMBER1 Negatively Regulates the OsMKKK10-OsMKK4-OsMPK6 Cascade to Coordinate the Trade-off between Grain Number per Panicle and Grain Size in Rice

Grain number and size are interactive agronomic traits that determine grain yield. However, the molecular mechanisms responsible for coordinating the trade-off between these traits remain elusive. Here, we characterized the rice (Oryza sativa) grain size and number1 (gsn1) mutant, which has larger grains but sparser panicles than the wild type due to disordered localized cell differentiation and proliferation. GSN1 encodes the mitogen-activated protein kinase phosphatase OsMKP1, a dual-specificity phosphatase of unknown function. Reduced expression of GSN1 resulted in larger and fewer grains, whereas increased expression resulted in more grains but reduced grain size. GSN1 directly interacts with and inactivates the mitogen-activated protein kinase OsMPK6 via dephosphorylation. Consistent with this finding, the suppression of mitogen-activated protein kinase genes OsMPK6, OsMKK4, and OsMKKK10 separately resulted in denser panicles and smaller grains, which rescued the mutant gsn1 phenotypes. Therefore, OsMKKK10-OsMKK4-OsMPK6 participates in panicle morphogenesis and acts on a common pathway in rice. We confirmed that GSN1 is a negative regulator of the OsMKKK10-OsMKK4-OsMPK6 cascade that determines panicle architecture. The GSN1-MAPK module coordinates the trade-off between grain number and grain size by integrating localized cell differentiation and proliferation. These findings provide important insights into the developmental plasticity of the panicle and a potential means to improve crop yields.

The QTL GNP1 Encodes GA20ox1, Which Increases Grain Number and Yield by Increasing Cytokinin Activity in Rice Panicle Meristems

Cytokinins and gibberellins (GAs) play antagonistic roles in regulating reproductive meristem activity. Cytokinins have positive effects on meristem activity and maintenance. During inflorescence meristem development, cytokinin biosynthesis is activated via a KNOX-mediated pathway. Increased cytokinin activity leads to higher grain number, whereas GAs negatively affect meristem activity. The GA biosynthesis genes GA20oxs are negatively regulated by KNOX proteins. KNOX proteins function as modulators, balancing cytokinin and GA activity in the meristem. However, little is known about the crosstalk among cytokinin and GA regulators together with KNOX proteins and how KNOX-mediated dynamic balancing of hormonal activity functions. Through map-based cloning of QTLs, we cloned a GA biosynthesis gene, Grain Number per Panicle1 (GNP1), which encodes rice GA20ox1. The grain number and yield of NIL-GNP1^TQ were significantly higher than those of isogenic control (Lemont). Sequence variations in its promoter region increased the levels of GNP1 transcripts, which were enriched in the apical regions of inflorescence meristems in NIL-GNP1^TQ. We propose that cytokinin activity increased due to a KNOX-mediated transcriptional feedback loop resulting from the higher GNP1 transcript levels, in turn leading to increased expression of the GA catabolism genes GA2oxs and reduced GA₁ and GA₃ accumulation. This rebalancing process increased cytokinin activity, thereby increasing grain number and grain yield in rice. These findings uncover important, novel roles of GAs in rice florescence meristem development and provide new insights into the crosstalk between cytokinin and GA underlying development process.

Grain number per panicle, a valuable agronomic trait for rice yield improvement, is profoundly affected by reproductive meristem activity. This activity, in turn, is controlled by transcriptional and plant hormone regulators, especially KNOX proteins and cytokinins. However, little is known about the roles of GAs in these processes in rice and how the regulatory network functions due to the complexity of crosstalk between plant hormone regulators. In this study, we identify a novel GA biosynthesis gene in rice and demonstrate its role in improving grain number and grain yield. We also propose that the KNOX-mediated cytokinin-GA activity rebalancing mechanisms regulate inflorescence meristem development and maintenance processes, providing a possible tool for high-yield rice breeding.

OsHAL3, a Blue Light-Responsive Protein, Interacts with the Floral Regulator Hd1 to Activate Flowering in Rice

In flowering plants, photoperiodic flowering is controlled by a complicated network. Light is one of the most important environmental stimuli that control the timing of the transition from vegetative growth to reproductive development. Several photoreceptors, including PHYA, PHYB, CRY2, and FKF1 in Arabidopsis and their homologs (OsPHYA, OsPHYB, OsPHYC, and OsCRY2) in rice, have been identified to be related to flowering. Our previous study suggests that OsHAL3, a flavin mononucleotide-binding protein, may function as a blue-light sensor. Here, we report the identification of OsHAL3 as a positive regulator of flowering in rice. OsHAL3 overexpression lines exhibited an early flowering phenotype, whereas downregulation of OsHAL3 expression by RNA interference delayed flowering under an inductive photoperiod (short-day conditions). The change in flowering time was not accompanied by altered Hd1 expression but rather by reduced accumulation of Hd3a and MADS14 transcripts. OsHAL3 and Hd1 colocalized in the nucleus and physically interacted in vivo under the dark, whereas their interaction was inhibited by white or blue light. Moreover, OsHAL3 directly bound to the promoter of Hd3a, especially before dawn. We conclude that OsHAL3, a novel light-responsive protein, plays an essential role in photoperiodic control of flowering time in rice, which is probably mediated by forming a complex with Hd1. Our findings open up new perspectives on the photoperiodic flowering pathway.

The miR156-SPL9-DFR pathway coordinates the relationship between development and abiotic stress tolerance in plants

Young organisms have relatively strong resistance to diseases and adverse conditions. When confronted with adversity, the process of development is delayed in plants. This phenomenon is thought to result from the rebalancing of energy, which helps plants to coordinate the relationship between development and stress tolerance; however, the molecular mechanism underlying this phenomenon remains mysterious. In this study, we found that miR156 integrates environmental signals to ensure timely flowering, thus enabling the completion of breeding. Under stress conditions, miR156 is induced to maintain the plant in the juvenile state for a relatively long period of time, whereas under favorable conditions, miR156 is suppressed to accelerate the developmental transition. Blocking the miR156 signaling pathway in Arabidopsis thaliana with 35S::MIM156 (via target mimicry) increased the sensitivity of the plant to stress treatment, whereas overexpression of miR156 increased stress tolerance. In fact, this mechanism is also conserved in Oryza sativa (rice). We also identified downstream genes of miR156, i.e. SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 9 (SPL9) and DIHYDROFLAVONOL-4-REDUCTASE (DFR), which take part in this process by influencing the metabolism of anthocyanin. Our results uncover a molecular mechanism for plant adaptation to the environment through the miR156-SPLs-DFR pathway, which coordinates development and abiotic stress tolerance.

The miR156-SPL9-DFR pathway coordinates the relationship between development and abiotic stress tolerance in plants

Young organisms have relatively strong resistance to diseases and adverse conditions. When confronted with adversity, the process of development is delayed in plants. This phenomenon is thought to result from the rebalancing of energy, which helps plants to coordinate the relationship between development and stress tolerance; however, the molecular mechanism underlying this phenomenon remains mysterious. In this study, we found that miR156 integrates environmental signals to ensure timely flowering, thus enabling the completion of breeding. Under stress conditions, miR156 is induced to maintain the plant in the juvenile state for a relatively long period of time, whereas under favorable conditions, miR156 is suppressed to accelerate the developmental transition. Blocking the miR156 signaling pathway in Arabidopsis thaliana with 35S::MIM156 (via target mimicry) increased the sensitivity of the plant to stress treatment, whereas overexpression of miR156 increased stress tolerance. In fact, this mechanism is also conserved in Oryza sativa (rice). We also identified downstream genes of miR156, i.e. SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 9 (SPL9) and DIHYDROFLAVONOL-4-REDUCTASE (DFR), which take part in this process by influencing the metabolism of anthocyanin. Our results uncover a molecular mechanism for plant adaptation to the environment through the miR156-SPLs-DFR pathway, which coordinates development and abiotic stress tolerance.

Genetic and physiological analysis of a novel type of interspecific hybrid weakness in rice

Hybrid weakness is an important reproductive barrier that hinders genetic exchange between different species at the post-zygotic stage. However, our understanding of the molecular mechanisms underlying hybrid weakness is limited. In this study, we report discovery of a novel interspecific hybrid weakness in a rice chromosome segment substitution line (CSSL) library derived from a cross between the indica variety Teqing (Oryza sativa) and common wild rice (O. rufipogon). The dominant Hybrid weakness i1 (Hwi1) gene from wild rice is genetically incompatible with Teqing and induced a set of weakness symptoms, including growth suppression, yield decrease, impaired nutrient absorption, and the retardation of crown root initiation. Phytohormone treatment showed that salicylic acid (SA) could restore the height of plants expressing hybrid weakness, while other phytohormones appear to have little effect. Fine mapping indicated that Hwi1 is located in a tandem leucine-rich repeat receptor-like kinase (LRR-RLK) gene cluster. Within the 13.2-kb candidate region on the short arm of chromosome 11, there are two annotated LRR-RLK genes, LOC_Os11g07230 and LOC_Os11g07240. The Teqing allele of LOC_Os11g07230 and the wild rice allele of LOC_Os11g07240 encode predicted functional proteins. Based on the genetic inheritance of hybrid weakness, LOC_Os11g07240 is implicated as the candidate gene for Hwi1. Functional analysis of Hwi1 will expand our knowledge of the regulation of hybrid weakness in rice.

Identification of quantitative trait Loci for lipid metabolism in rice seeds

Plant seed oil is important for human dietary consumption and industrial application. The oil trait is controlled by quantitative trait loci (QTLs), but no QTLs for fatty acid composition are known in rice, the monocot model plant. QTL analysis was performed using F(2) and F(2:3) progeny from a cross of an indica variety and a japonica variety. Gas chromatography-mass spectrometry (GC-MS) analysis revealed significant differences between parental lines in fatty acid composition of brown rice oil, and 29 associated QTLs in F(2) and/or F(2:3) populations were identified throughout the rice genome, except chromosomes 9 and 10. Eight QTLs were repeatedly identified in both populations across different environments. Five loci pleiotropically controlled different traits, contributing to complex interactions of oil with fatty acids and between fatty acids. Nine rice orthologs of Arabidopsis genes encoding key enzymes in lipid metabolism co-localized with 11 mapped QTLs. A strong QTL for oleic (18:1) and linoleic (18:2) acid were associated with a rice ortholog of a gene encoding acyl-CoA:diacylglycerol acyltransferase (DGAT), and another for palmitic acid (16:0) mapped similarly to the acyl-ACP thioesterase (FatB) gene ortholog. Our approach rapidly and efficiently identified candidate genes for mapped QTLs controlling fatty acid composition and oil concentration, providing information for improving rice grain quality by marker assisted selection.

Rice carotenoid β-ring hydroxylase CYP97A4 is involved in lutein biosynthesis

Lutein is the most abundant plant carotenoid and plays essential roles in photosystem assembly and stabilization, as well as protection against photostress. To date, only a few lutein biosynthesis genes have been identified in crop plants. In this study, the rice Cyt P450 gene CYP97A4 encoding a carotenoid β-ring hydroxylase was shown to be involved in lutein biosynthesis. The results revealed that CYP97A4 was preferentially expressed in leaf compared with spikelet, sheath, stalk and root, and encoded a protein localized at the subcellular level to the chloroplasts. Compared with the wild type, the three allelic mutants of CYP97A4 displayed lutein reductions of 12-24% with substantially increased α-carotene, while Chl a/b levels were unaltered. The increased α-carotene in the mutants led to greater sensitivity under high light stress. Similarly, reactive oxygen species (ROS) imaging of leaves treated with intense light showed that the mutants generally accumulated greater levels of ROS compared with wild-type plants, which probably caused detrimental effects to the plant photosystem. In conclusion, this study demonstrated the important role of CYP97A4 in α-carotene hydroxylation in rice, and knock-out of the gene reduced lutein and increased α-carotene, contributing to sensitivity to intense light.

Fine mapping and candidate gene analysis of spd6, responsible for small panicle and dwarfness in wild rice (Oryza rufipogon Griff.)

Identification of genes in rice that affect production and quality is necessary for improving the critical global food source. CSSL58, a chromosome segment substitution line (CSSL) containing a chromosome segment of Oryza rufipogon in the genetic background of the indica cultivar Teqing showed significantly smaller panicles, fewer grains per panicle, smaller grains and dwarfness compared with the recurrent parent Teqing. Genetic analysis of the BC(4)F(1) and BC(4)F(2) generations, derived from a cross between CSSL58 and Teqing, showed that these traits are controlled by the recessive gene spd6, which mapped to the short arm of chromosome 6. Fine mapping and high-resolution linkage analysis using 24,120 BC(4)F(3) plants and markers flanking spd6 were carried out, and the gene was localized to a 22.4 kb region that contains four annotated genes according to the genome sequence of japonica Nipponbare. Phenotypic evaluation of the nearly isogenic line NIL(spd6) revealed that spd6 from wild rice has pleiotropic effects on panicle number per plant, grain size, grain weight, grain number per panicle and plant height, suggesting that this gene might play an important role in the domestication of rice. The discovery of spd6 may ultimately be useful for the design and breeding of crops with high grain yield and quality.

[Clinical characteristics and prevention of positive stump in gastric cancer]

This paper summarizes 80 cases with positive stump among 946 cases of gastric cancer treated by gastrectomy from 1962 to 1986. The positive stump rate was much higher at the esophageal than the duodenal end (12.5% vs 4.5%). It was related to gross type and size of cancer (P less than 0.01). In lesions larger than 5 cm in diameter and of infiltrating type, especially the superficially spreading early cancers by which the gastric mucosa was infiltrated extensively without any clear margin, it was difficult to identify the extent of infiltration and cancer residue due to inadequate resection was likely. In order to avoid a positive stump, 1. total gastrectomy is indicated for cancer of the gastric body or infiltrating type, 2. super-subtotal gastrectomy including the whole lesser curvature or total gastrectomy is indicated for localized lesions larger than 5 cm in diameter at the antrum, and 3. for proximal cancers, the resection line should be set in the esophagus 5 cm beyond the tumor margin and routine examination of the resected specimen should be done during the operation.

[Cause and surgical management of local recurrence of rectal cancer following radical resection retaining the anus]

Of seventy-one patients with rectal cancer after radical resection retaining the anus, 15 developed local recurrence with a recurrence rate of 21.1%. Local recurrence was correlated with improper safety margin from the lower edge of cancer to the anal end. There was statistical significant difference between 3 cm or more and 2 cm or less. The local recurrence was also related to the pathologic stage, histologic differentiation and implant of free cancer cells. It is suggested that the surgical indication of saving the anus be strict and without stretching, the safety margin from the lower edge of cancer to the anal end should not be less than 2 cm in early rectal cancer and not less than 4 cm in advanced lesions. During the operation, no touching tumor technique, thorough rinsing of the peritoneal cavity and pre- or post-operative radiotherapy are important for prevention of local recurrence. Early local recurrent rectal cancer can be detected by periodic examinations.

[Indication of radical surgery (R2, R3) based upon the pattern of lymph node metastasis from gastric cancer]

From Jan. 1980 to June. 1984, radical operation was performed in 156 patients with gastric cancer according to the "protocol" introduced by the Gastric Cancer Research Society of Japan. There were 24 early and 132 advanced gastric cancers. Seventy patients were treated by type R2, 86 by R+2 and R3. Radical distal subtotal gastrectomy was done in 116, proximal subtotal gastrectomy in 7, simple total gastrectomy in 13 and subtotal or total gastrectomy combined with neighbouring organ resection in 20. According to TNM staging, 24 (15.4%) lesions were stage I, 9 (5.8%) stage II, 100 (64.1%) stage III and 23 (14.7%) stage IV. Twenty four lesions were within the mucosa or submucosal layer, 11 in proprius muscle layer, 18 to subserosa, 15 to serosa, 46 beyond serosa, 42 involving the surrounding organs. Lymph node metastatic rate was 66% (103 cases), metastatic degree was 21.5% (558/2593). The metastatic degree of lymph node line I, II and III was 24.7%, 20% and 8.3%, respectively. Basing on lymph node metastatic rate and degree as well as the line degree, it is proposed that, in the early stage of gastric cancer, type R1 be performed for cancer limited to the mucosa, especially the minute type, R2 for cancer invading the submucosa, in which, R+2 be indicated for some isolated patients. In the advanced gastric cancer, type R+2 be performed in the majority of patients and R3 in a few. R3 or total gastrectomy combined with neighbouring organ resection be carried out only in a part of cases with the limited type infiltrating beyond the serosa or invading the neighbouring organs.