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One of the most critical steps in cereal threshing is the ease with which seeds are detached from sticky glumes. Naked grains with low glume coverage have dramatically increased threshing efficiency and seed quality. Here, we demonstrate that GC1 ( Glume Coverage 1 ), encoding an atypical G protein γ subunit, negatively regulates sorghum glume coverage. Naturally truncated variations of GC1 C-terminus accumulate at higher protein levels and affect the stability of a patatin-related phospholipase SbpPLAII-1. A strong positive selection signature around the GC1 genic region is found in the naked sorghum cultivars. Our findings reveal a crucial event during sorghum domestication through a subtle regulation of glume development by GC1 C-terminus variation, and establish a strategy for future breeding of naked grains. Low glume coverage is the preferred for easy threshing in grain production, but the genetic basis remains unclear. Here, the authors report the gene GC1 , which encodes an atypical G protein γ subunit, negatively regulates sorghum glume coverage and the naturally truncated alleles can be useful in the naked grain breeding.

Crossing wild and domestic rice often results in hybrid sterility. Such genetic barriers can prevent the movement of potentially beneficial genes from wild rice into domestic varieties. To understand the barriers preventing gene flow, Yu et al. mapped a quantitative trait locus (QTL) that determines sterility between wild-type and domestic rice. This QTL encodes two open reading frames (ORFs) that are both expressed during gametogenesis. The ORFs encode a toxin, which affects the development of pollen, and an antidote, which is required for pollen viability. Thus, selfish genetic elements can underlie evolutionary strategies that facilitate reproductive isolation. Science , this issue p. 1130 A toxin-antidote system with a role in postzygotic reproductive isolation of different wild and cultivated rice species is described. Selfish genetic elements are pervasive in eukaryote genomes, but their role remains controversial. We show that qHMS7 , a major quantitative genetic locus for hybrid male sterility between wild rice ( Oryza meridionalis ) and Asian cultivated rice ( O. sativa ), contains two tightly linked genes [ Open Reading Frame 2 ( ORF2 ) and ORF3 ]. ORF2 encodes a toxic genetic element that aborts pollen in a sporophytic manner, whereas ORF3 encodes an antidote that protects pollen in a gametophytic manner. Pollens lacking ORF3 are selectively eliminated, leading to segregation distortion in the progeny. Analysis of the genetic sequence suggests that ORF3 arose first, followed by gradual functionalization of ORF2 . Furthermore, this toxin-antidote system may have promoted the differentiation and/or maintained the genome stability of wild and cultivated rice.

Background/Objectives: In crop genetic engineering, morphogenic genes have attracted increasing attention, given their ability to facilitate the transformation of a broad range of otherwise nontransformable cultivars. However, few callus-specific promoters have been identified to date that can be employed to avoid the adverse effects resulting from the ectopic expression of morphogenic genes on shoot regeneration and growth. Methods: A set of potential callus-specific genes were initially selected based on publicly available data. These genes were then screened using quantitative real-time polymerase chain reaction (qPCR), followed by promoter activity evaluation using a transgenic approach with the GUS gene serving as a reporter. Results: Of the 24 evaluated promoters, 12 were verified as being callus-specific using qPCR. Five genes (Os11g0295900, Os10g0207500, Os01g0300000, Os02g0252200, and Os04g0488100) were chosen, and their promoters were cloned. Based on GUS staining, the pOsTDL1B (Os10g0207500) promoter showed strong callus-specific expression, pOsEDC (Os01g0300000) was a medium-level callus-specific promoter, and pOsDLN53 (Os02g0252200) was strictly callus-specific, although its activity was low. Quantification of GUS activity indicated that all three pOsTDL1B:GUS transgenic lines exhibited strong callus specificity relative to the various tissues tested. Conclusions: A callus-specific promoter was identified that can be used to drive the expression of morphogenic genes in crop transformation.

Panicle size is a critical determinant of grain yield in rice (Oryza sativa) and other grain crops. During rice growth and development, spikelet abortion often occurs at either the top or the basal part of the panicle under unfavorable conditions, causing a reduction in fertile spikelet number and thus grain yield. In this study, we report the isolation and functional characterization of a panicle abortion mutant named panicle apical abortion1-1 (paab1-1). paab1-1 exhibits degeneration of spikelets on the apical portion of panicles during late stage of panicle development. Cellular and physiological analyses revealed that the apical spikelets in the paab1-1 mutant undergo programmed cell death, accompanied by nuclear DNA fragmentation and accumulation of higher levels of H2O2 and malondialdehyde. Molecular cloning revealed that paab1-1 harbors a mutation in OsALMT7, which encodes a putative aluminum-activated malate transporter (OsALMT7) localized to the plasma membrane, and is preferentially expressed in the vascular tissues of developing panicles. Consistent with a function for OsALMT7 as a malate transporter, the panicle of the paab1-1 mutant contained less malate than the wild type, particularly at the apical portions, and injection of malate into the paab1-1 panicle could alleviate the spikelet degeneration phenotype. Together, these results suggest that OsALMT7-mediated transport of malate into the apical portion of panicle is required for normal panicle development, thus highlighting a key role of malate in maintaining the sink size and grain yield in rice and probably other grain crops.

Liu et al. provide new resources for improving rice by cloning a gene cluster that enhances resistance to two species of planthoppers, which cause billions of dollars of crop loss. The brown planthopper (BPH) is the most destructive pest of rice ( Oryza sativa ) and a substantial threat to rice production, causing losses of billions of dollars annually 1 , 2 . Breeding of resistant cultivars is currently hampered by the rapid breakdown of BPH resistance 2 . Thus, there is an urgent need to identify more effective BPH-resistance genes. Here, we report molecular cloning and characterization of Bph3 , a locus in rice identified more than 30 years ago that confers resistance to BPH. We show that Bph3 is a cluster of three genes encoding plasma membrane–localized lectin receptor kinases (OsLecRK1-OsLecRK3). Introgression of Bph3 into susceptible rice varieties by transgenic or marker-assisted selection strategies significantly enhanced resistance to both the BPH and the white back planthopper. Our results suggest that these lectin receptor kinase genes function together to confer broad-spectrum and durable insect resistance and provide a resource for molecular breeding of insect-resistant rice cultivars.

Foxtail millet ( Setaria italica ) is an important crop species and an emerging model plant for C 4 grasses. However, functional genomics research on foxtail millet is challenging because of its long generation time, relatively large stature and recalcitrance to genetic transformation. Here we report the development of xiaomi , a rapid-cycling mini foxtail millet mutant as a C 4 model system. Five to six generations of xiaomi can be grown in a year in growth chambers due to its short life cycle and small plant size, similar to Arabidopsis . A point mutation in the Phytochrome C ( PHYC ) gene was found to be causal for these characteristics. PHYC encodes a light receptor essential for photoperiodic flowering. A reference-grade xiaomi genome comprising 429.94 Mb of sequence was assembled and a gene-expression atlas from 11 different tissues was developed. These resources, together with an established highly efficient transformation system and a multi-omics database, make xiaomi an ideal model system for functional studies of C 4 plants. This study developed xiaomi , a mini foxtail millet mutant, as a C 4 model plant that has a short life cycle and small stature. To further enhance its model plant function, xiaomi ’s genome was sequenced and an efficient transformation system was established.

Strigolactones (SLs), a newly discovered class of carotenoid-derived phytohormones, are essential for developmental processes that shape plant architecture and interactions with parasitic weeds and symbiotic arbuscular mycorrhizal fungi. Despite the rapid progress in elucidating the SL biosynthetic pathway, the perception and signalling mechanisms of SL remain poorly understood. Here we show that DWARF 53 (D53) acts as a repressor of SL signalling and that SLs induce its degradation. We find that the rice ( Oryza sativa ) d53 mutant, which produces an exaggerated number of tillers compared to wild-type plants, is caused by a gain-of-function mutation and is insensitive to exogenous SL treatment. The D53 gene product shares predicted features with the class I Clp ATPase proteins and can form a complex with the α/β hydrolase protein DWARF 14 (D14) and the F-box protein DWARF 3 (D3), two previously identified signalling components potentially responsible for SL perception. We demonstrate that, in a D14- and D3-dependent manner, SLs induce D53 degradation by the proteasome and abrogate its activity in promoting axillary bud outgrowth. Our combined genetic and biochemical data reveal that D53 acts as a repressor of the SL signalling pathway, whose hormone-induced degradation represents a key molecular link between SL perception and responses. Strigolactones (SLs), key regulators of plant growth, are believed to mediate their responses through a proposed receptor (D14) that interacts with an F-box protein (D3) to form a D14–SCF D3 protein complex; here the perception of SLs by the D14–SCF D3 complex and the control of gene expression are linked by the finding that DWARF 53, a repressor protein of SL function, interacts with the D14–SCF D3 complex and is ubiquitinated and degraded in a SL-dependent manner. Strigolactone receptor identified The strigolactones are key regulators of plant growth, controlling the formation of secondary shoots and regulating root branching. Strigolactone responses are mediated through a proposed receptor (D14) that interacts with an F-box protein (D3). Now, in two related publications, Liang Jiang et al . and Feng Zhou et al . demonstrate a functional link between the perception of strigolactones by D14/D3 and the control of gene expression in rice. They show that the protein DWARF53 (D53), of previously unknown function, acts as a repressor of strigolactone signalling and that strigolactones induce its degradation. D53 interacts with the D14–D3 complex and is ubiquitinated and degraded by the proteasome in a strigolactone-dependent manner.

Understanding the molecular mechanisms that regulate grain yield is important for improving agricultural productivity. Protein ubiquitination controls various aspects of plant growth but lacks understanding on how E2-E3 enzyme pairs impact grain yield in major crops. Here, we identified a RING-type E3 ligase SGD1 and its E2 partner SiUBC32 responsible for grain yield control in Setaria italica . The conserved role of SGD1 was observed in wheat, maize, and rice. Furthermore, SGD1 ubiquitinates the brassinosteroid receptor BRI1, stabilizing it and promoting plant growth. Overexpression of an elite SGD1 haplotype improved grain yield by about 12.8% per plant, and promote complex biological processes such as protein processing in endoplasmic reticulum, stress responses, photosystem stabilization, and nitrogen metabolism. Our research not only identifies the SiUBC32-SGD1-BRI1 genetic module that contributes to grain yield improvement but also provides a strategy for exploring key genes controlling important traits in Poaceae crops using the Setaria model system. Researchers identify an E3 ligase SGD1 and its E2 partner responsible for grain yield control using foxtail millet, and reveal its conserved role in wheat, maize, and rice. Furthermore, SGD1 ubiquitinates the brassinosteroid receptor BRI1 thus stabilizing it and promoting grain yield in crops.

Success of modern agriculture relies heavily on breeding of crops with maximal regional adaptability and yield potentials. A major limiting factor for crop cultivation is their flowering time, which is strongly regulated by day length (photoperiod) and temperature. Here we report identification and characterization of Days to heading 7 ( DTH7 ), a major genetic locus underlying photoperiod sensitivity and grain yield in rice. Map-based cloning reveals that DTH7 encodes a pseudo-response regulator protein and its expression is regulated by photoperiod. We show that in long days DTH7 acts downstream of the photoreceptor phytochrome B to repress the expression of Ehd1 , an up-regulator of the “florigen” genes ( Hd3a and RFT1 ), leading to delayed flowering. Further, we find that haplotype combinations of DTH7 with Grain number, plant height, and heading date 7 ( Ghd7 ) and DTH8 correlate well with the heading date and grain yield of rice under different photoperiod conditions. Our data provide not only a macroscopic view of the genetic control of photoperiod sensitivity in rice but also a foundation for breeding of rice cultivars better adapted to the target environments using rational design. Significance Flowering time is one of the best studied ecologically important traits under natural or human selection for adaptation of plants to specific local environments. Photoperiodic sensitivity is a major agronomic trait that tailors vegetative and reproductive growth to local climates and is thus particularly important for crop yield and quality. This study not only identifies a major quantitative trait locus underlying photoperiod sensitivity in rice ( Days to heading 7 , DTH7 ) but also demonstrates that various haplotype combinations of DTH7 with Grain number, plant height, and heading date 7 ( Ghd7 ) and DTH8 correlate well with the flowering time and grain yield of rice varieties under diverse cultivating conditions. Our results build a foundation for breeding of high-yield rice varieties with desired photosensitivity and optimum adaptation to the target environments.

Breakdown of reproductive isolation facilitates flow of useful trait genes into crop plants from their wild relatives. Hybrid sterility, a major form of reproductive isolation exists between cultivated rice ( Oryza sativa ) and wild rice ( O. meridionalis , Mer ). Here, we report the cloning of qHMS1 , a quantitative trait locus controlling hybrid male sterility between these two species. Like qHMS7 , another locus we cloned previously, qHMS1 encodes a toxin-antidote system, but differs in the encoded proteins, their evolutionary origin, and action time point during pollen development. In plants heterozygous at qHMS1 , ~ 50% of pollens carrying qHMS1- D (an allele from cultivated rice) are selectively killed. In plants heterozygous at both qHMS1 and qHMS7,  ~ 75% pollens without co-presence of qHMS1-Mer and qHMS7- D are selectively killed, indicating that the antidotes function in a toxin-dependent manner. Our results indicate that different toxin-antidote systems provide stacked reproductive isolation for maintaining species identity and shed light on breakdown of hybrid male sterility. Orzya meridionalis is a wild rice species that has reproductive isolation with Asian cultivated rice. Here, the authors report the cloning of the second locus controlling hybrid male sterility between the two species and show the encoded toxin-antidote system provides stacked reproductive isolation for maintaining species identity.