Artificial selection of the Green Revolution gene Semidwarf 1 is implicated in upland rice breeding

Semidwarf breeding has boosted crop production and is a well-known outcome from the first Green Revolution. The Green Revolution gene Semidwarf 1(SD1), which modulates gibberellic acid(GA) biosynthesis, plays a principal role in determining rice plant height. Mutations in SD1 reduce rice plant height and promote lodging resistance and fertilizer tolerance to increase grain production. The plant height mediated by SD1 also favors grain yield under certain conditions. However, it is not yet known whether the function of SD1 in upland rice promotes adaptation and grain production. In this study, the plant height and grain yield of irrigated and upland rice were comparatively analyzed under paddy and dryland conditions. In response to dryland environments, rice requires a reduction in plant height to cope with water deficits. Upland rice accessions had greater plant heights than their irrigated counterparts under both paddy and dryland conditions, and appropriately reducing plant height could improve adaptability to dryland environments and maintain high grain yield formation. Moreover, upland rice cultivars with thicker stem diameters had stronger lodging resistance, which addresses the lodging problem. Knockout of SD1 in the upland rice cultivar IRAT104 reduced the plant height and grain yield, demonstrating that the adjustment of plant height mediated by SD1 could increase grain production in dryland fields. In addition, an SD1 genetic diversity analysis verified that haplotype variation causes phenotypic variation in plant height. During the breeding history of rice, SD1 allelic mutations were selected from landraces to improve the grain yield of irrigated rice cultivars, and this selection was accompanied by a reduction in plant height. Thus, five known mutant alleles were analyzed to verify that functional SD1 is required for upland rice production. All these results suggest that SD1 might have undergone artificial positive selection in upland rice, which provides further insights concerning greater plant height in upland rice breeding.

The ABA synthesis enzyme allele OsNCED2^(T)promotes dryland adaptation in upland rice

Upland rice shows dryland adaptation in the form of a deeper and denser root system and greater drought resistance than its counterpart,irrigated rice.Our previous study revealed a difference in the frequency of the OsNCED2 gene between upland and irrigated populations.A nonsynonymous mutation(C to T,from irrigated to upland rice)may have led to functional variation fixed by artificial selection,but the exact biological function in dryland adaptation is unclear.In this study,transgenic and association analysis indicated that the domesticated fixed mutation caused functional variation in OsNCED2,increasing ABA levels,root development,and drought tolerance in upland rice under dryland conditions.OsNCED2-overexpressing rice showed increased reactive oxygen species-scavenging abilities and transcription levels of many genes functioning in stress response and development that may regulate root development and drought tolerance.OsNCED2^(T)-NILs showed a denser root system and drought resistance,promoting the yield of rice under dryland conditions.OsNCED2^(T)may confer dryland adaptation in upland rice and may find use in breeding dryland-adapted,water-saving rice.

Developing superior alleles of yield genes in rice by artificial mutagenesis using the CRISPR/Cas9 system

Rice yield is an important and complex agronomic trait controlled by multiple genes.In recent decades,dozens of yield-associated genes in rice have been cloned,many of which can increase production in the form of loss or degeneration of function.However,mutations occurring randomly under natural conditions have provided very limited genetic resources for yield increases.In this study,potentially yield-increasing alleles of two genes closely associated with yield were edited artificially.The recently developed CRISPR/Cas9system was used to edit two yield genes:Grain number 1a(Gn1a)and DENSE AND ERECT PANICLE1(DEP1).Several mutants were identified by a target sequence analysis.Phenotypic analysis confirmed one mutant allele of Gn1a and three of DEP1 conferring yield superior to that conferred by other natural high-yield alleles.Our results demonstrate that favorable alleles of the Gnla and DEP1 genes,which are considered key factors in rice yield increases,could be developed by artificial mutagenesis using genome editing technology.

长雄野生稻有利基因的发掘与利用

人类将普通野生稻驯化为亚洲栽培稻,其农艺性状如株高、落粒性、穗型等发生了重要变化,产量也大幅提高,但许多优良性状如抗逆性等却丢失。长雄野生稻与亚洲栽培稻同属AA基因组,蕴藏了许多生物胁迫和非生物胁迫的抗性基因,被认为是亚洲栽培稻遗传改良的潜在基因库。本文总结了长雄野生稻生物及非生物胁迫抗性、地下茎性状以及其他潜在应用价值性状,包括白叶枯抗性、抗旱性、耐热性、自交不亲和性、氮高效利用以及高产等有利性状。基于长雄野生稻地下茎性状开展多年生稻育种实践的应用研究,对长雄野生稻进行从头驯化的策略进行了探讨,以期为长雄野生稻基础研究及栽培稻遗传改良提供理论参考。

Differential microRNA expression between shoots and rhizomes in Oryza longistaminata using high-throughput RNA sequencing

Plant microRNAs(miRNAs)play important roles in biological processes such as development and stress responses.Although the diverse functions of miRNAs in model organisms have been well studied,their function in wild rice is poorly understood.In this study,high-throughput small RNA sequencing was performed to characterize tissue-specific transcriptomes in Oryza longistaminata.A total of 603 miRNAs,380 known rice miRNAs,72 conserved plant miRNAs,and151 predicted novel miRNAs were identified as being expressed in aerial shoots and rhizomes.Additionally,99 and 79 miRNAs were expressed exclusively or differentially,respectively,in the two tissues,and 144 potential targets were predicted for the differentially expressed miRNAs in the rhizomes.Functional annotation of these targets suggested that transcription factors,including squamosa promoter binding proteins and auxin response factors,function in rhizome growth and development.The expression levels of several miRNAs and target genes in the rhizomes were quantified by RT-PCR,and the results indicated the existence of complex regulatory mechanisms between the miRNAs and their targets.Eight target cleavage sites were verified by RNA ligase-mediated rapid 5′end amplification.These results provide valuable information on the composition,expression and function of miRNAs in O.longistaminata,and will aid in understanding the molecular mechanisms of rhizome development.

Identification of Key Genes for the Ultrahigh Yield of Rice Using Dynamic Cross-tissue Network Analysis

Significantly increasing crop yield is a major and worldwide challenge for food supply and security.It is well-known that rice cultivated at Taoyuan in Yunnan of China can produce the highest yield worldwide.Yet,the gene regulatory mechanism underpinning this ultrahigh yield has been a mystery.Here,we systematically collected the transcriptome data for seven key tissues at different developmental stages using rice cultivated both at Taoyuan as the case group and at another regular rice planting place Jinghong as the control group.We identified the top 24 candidate high-yield genes with their network modules from these well-designed datasets by developing a novel computational systems biology method,i.e.,dynamic cross-tissue(DCT)network analysis.We used one of the candidate genes,Os SPL4,whose function was previously unknown,for gene editing experimental validation of the high yield,and confirmed that Os SPL4 significantly affects panicle branching and increases the rice yield.This study,which included extensive field phenotyping,cross-tissue systems biology analyses,and functional validation,uncovered the key genes and gene regulatory networks underpinning the ultrahigh yield of rice.The DCT method could be applied to other plant or animal systems if different phenotypes under various environments with the common genome sequences of the examined sample.DCT can be downloaded from https://github.com/ztpub/DCT.

Genome and Comparative Transcriptomics of African Wild Rice Oryza Iongistaminata Provide Insights into Molecular Mechanism of Rhizomatousness and Self-Incompatibility

Dear Editor, Oryza Iongistaminata is an African wild rice species with AA genome type possessing special traits that are highly valued for improving cultivated rice, such as strong resistance to biotic and abiotic stresses （Song et al., 1995） for improving resistance of cultivars, rhizomatousness for perennial breeding （Glover et al., 2010）, and self-incompatibility （SI） for new ways to produce hybrid seeds （Ghesquiere, 1986）. Deciphering the genome of O. Iongistaminata will be the key to uncovering the mechanism of these hallmark traits and improving cultivated rice.

Alternative splicing drives the functional diversification of a b HLH transcription factor in the control of growth and drought tolerance in rice

Given the increase in global climate change,reconciling the increasing demand for food production with dwindling water resources poses a formidable challenge.To ensure sustainable rice production and global food security,a thorough exploration of the genetic mechanism that underlies the delicate balance between growth and drought tolerance in rice is imperative.The sessile nature of plants has driven their adaptive evolution,enabling them to regulate gene expression and exhibit physiological and developmental plasticity in response to environmental changes[1].Alternative splicing(AS),a prevalent phenomenon in plants,plays a crucial role in the regulation of posttranscriptional gene expression[2].AS serves as an essential mechanism involved in both developmental processes and stress responses[3–5].