New QTLs identified for leaf correlative traits in rice seedlings under cadmium stress

Cadmium (Cd) is a non-essential toxic metal that is primarily released into the environment from artificial sources in recent decades. To investigate the genetics of Cd toxicity tolerance at the seedling stage in rice, a QTL analysis was carried out under cadmium stress conditions with two toxicity-linked traits—leaf rolling (LR) and the green leaf ratio (GLR). Using 127 rice lines of doubled haploid (DH) population derived from a cross between a japonica JX17 and indica ZYQ8, two QTLs for LR (qLR-1 and qLR-9) and one QTL for GLR (qGLR-3) were detected. Among them, the phenotypic variation of qLR-1 and qGLR-3 were 19.27 and 16.09, values which are useful for marker-assistant selection in breeding elite rice cultivars that have the capacity to tolerate Cd. The results further demonstrate that visual measurements of both LR and GLR in seedlings are effective methods for screening tolerant rice germplasm in cadmium stress scenarios.     

Bone marrow endothelial progenitors in atherosclerotic plaque resolution

Atherosclerosis is a major cause of morbidity and mortality in the United States. Persistently elevated circulating low-density lipoprotein, or hypercholesterolemia, and deposition of low-density lipoprotein in the vascular wall are the main inducers of atherosclerosis, which manifests itself as arterial lesions or plaques. Some plaques become thrombosis-prone and rupture, causing acute myocardial infarction or stroke. Lowering plasma cholesterol through the use of statins is the primary intervention against atherosclerosis. Treatment with statins slows progression of atherosclerosis but can only support limited plaque regression. Partially regressed plaques continue to pose a serious threat due to their remaining potential to rupture. Thus, new interventions inducing complete reversal of atherosclerosis are being sought. Implementation of new therapies will require clear understanding of the mechanisms driving plaque resolution. In this Commentary, we highlight the role of bone marrow endothelial progenitors in atherosclerotic plaque regression and discuss how regenerative cell-based interventions could be used in combination with plasma lipid-lowering to induce plaque reversal in order to prevent and/or reduce adverse cardiovascular events.     

水稻突变体与功能基因组学

突变体是功能基因组学研究的重要材料。本文综述了水稻突变体的创制方法、变异的机制、水稻突变体/基因分类和数量、克隆的水稻重要基因的研究进展, 包括1 698个水稻突变体/基因的分类和43个克隆的水稻突变体基因, 并提出了利用水稻突变体的展望。     

一个新的水稻叶形突变体(tll1)的遗传分析与精细定位

利用甲基磺酸乙酯(ethylmethane sulphonate, EMS)诱变粳稻品种日本晴获得了一个遗传稳定的叶形突变体 thread-like leaf 1 (tll1)。该突变体在杭州表现为矮化、窄叶, 极端时仅剩主脉, 呈细丝状。将该突变体分别与籼稻品种南京6号、浙辐802和9311进行正反交配组, 遗传分析表明该突变体性状由1对隐性单基因控制。通过SSR和STS分子标记对F₂代分离群体进行遗传定位, 将该基因初步定位在第12染色体SSR标记RM247和RM101之间。随后利用已公布的粳稻品种日本晴和籼稻品种9311的基因组序列, 发展了7对有多态的STS标记, 最终将该基因定位在FL13和FL14之间约94.3 kb的区间内, 为进一步克隆TLL1基因奠定了基础。     

Disruption of EARLY LESION LEAF 1, encoding a cytochrome P450 monooxygenase,induces ROS accumulation and cell death in rice

Lesion-mimic mutants (LMMs) provide a valuable tool to reveal the molecular mechanisms determining programmed cell death (PCD) in plants. Despite intensive research, the mechanisms behind PCD and the formation of lesions in various LMMs still remain to be elucidated. Here, we identified a rice (Oryza sativa) LMM, early lesion leaf 1 (ell1), cloned the causal gene by map-based cloning, and verified this by complementation. ELL1 encodes a cytochrome P450 monooxygenase, and the ELL1 protein was located in the endoplasmic reticulum. The ell1 mutant exhibited decreased chlorophyll contents, serious chloroplast degradation, upregulated expression of chloroplast degradation-related genes, and attenuated photosynthetic protein activity, indicating that ELL1 is involved in chloroplast development. RNA sequencing analysis showed that genes related to oxygen binding were differentially expressed in ell1 and wild-type plants; histochemistry and paraffin sectioning results indicated that hydrogen peroxide (H₂O₂) and callose accumulated in the ell1 leaves, and the cell structure around the lesions was severely damaged, which indicated that reactive oxygen species (ROS) accumulated and cell death occurred in the mutant. TUNEL staining and comet experiments revealed that severe DNA degradation and abnormal PCD occurred in the ell1 mutants, which implied that excessive ROS accumulation may induce DNA damage and ROS-mediated cell death in the mutant. Additionally, lesion initiation in the ell1 mutant was light dependent and temperature sensitive. Our findings revealed that ELL1 affects chloroplast development or function, and that loss of ELL1 function induces ROS accumulation and lesion formation in rice.     

SEMI-ROLLED LEAF 10 stabilizes catalase isozyme B to regulate leaf morphology and thermotolerance in rice (Oryza sativa L.)

Plant architecture and stress tolerance play important roles in rice breeding. Specific leaf morphologies and ideal plant architecture can effectively improve both abiotic stress resistance and rice grain yield. However, the mechanism by which plants simultaneously regulate leaf morphogenesis and stress resistance remains elusive. Here, we report that SRL10, which encodes a double-stranded RNA-binding protein, regulates leaf morphology and thermotolerance in rice through alteration of microRNA biogenesis. The srl10 mutant had a semi-rolled leaf phenotype and elevated sensitivity to high temperature. SRL10 directly interacted with catalase isozyme B (CATB), and the two proteins mutually increased one other's stability to enhance hydrogen peroxide (H₂O₂) scavenging, thereby contributing to thermotolerance. The natural Hap3 (AGC) type of SRL10 allele was found to be present in the majority of aus rice accessions, and was identified as a thermotolerant allele under high temperature stress in both the field and the growth chamber. Moreover, the seed-setting rate was 3.19 times higher and grain yield per plant was 1.68 times higher in near-isogenic line (NIL) carrying Hap3 allele compared to plants carrying Hap1 allele under heat stress. Collectively, these results reveal a new locus of interest and define a novel SRL10–CATB based regulatory mechanism for developing cultivars with high temperature tolerance and stable yield. Furthermore, our findings provide a theoretical basis for simultaneous breeding for plant architecture and stress resistance.