Strigolactones (SLs) are a new class of carotenoid-derived phytohormones essential for developmental processes shaping 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 signaling mechanisms of SL remain poorly understood. Here we show that DWARF53 (D53) acts as a repressor of SL signaling and SLs induce its degradation. We found that the rice 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 DWARF14 (D14) and the F-box protein DWARF3 (D3), two previously identified signaling 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 signaling pathway, whose hormone-induced degradation represents a key molecular link between SL perception and responses.
nature biotechnology advance online publication l e t t e r sThe 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.BPH (Nilaparvata lugens Stål, Hemiptera, Delphacidae) is a monophagous, phloem-sucking herbivore. It sucks the sap from the rice phloem using its stylet, and causes direct damage to rice plants. BPH can also cause indirect damage to rice plants through the transmission of viruses including the rice ragged stunt virus and grassy stunt virus 2 . Repeated overapplication of pesticides for BPH management has heavily polluted the environment 3 . Breeding of resistant cultivars is the most cost-effective and environmentally responsible strategy for BPH management but developing insect resistant cultivars by traditional breeding approaches is extremely difficult and time consuming owing to a paucity of knowledge about BPH resistance genes and germplasm.To date, 28 BPH resistance loci have been identified from cultivated and wild species of Oryza 2,4,5 . Only two of these resistance genes, Bph14 and Bph26 have been cloned to date 6,7 . In addition, BPH resistance of IR26 and IR36, two widely cultivated rice varieties that harbor the BPH resistance loci Bph1 and bph2, respectively, was quickly broken down in just a few years owing to the rapid adaptation of the BPH 8 . Thus, there is still an urgent need to identify new types of resistance genes and germplasm for developing efficient approaches to breed broad-spectrum and durable BPH-resistant rice cultivars. Notably, the Bph3 locus, originally identified in the Sri Lankan indica cultivar Rathu Heenati 9 , displayed resistance to four BPH biotypes (BPH biotypes refer to specific populations of BPH classified according to their virulence on different BPH resistance genes) 2,10 . Furthermore, rice varieties harboring Bph3 deployed more than 30 years ago in the Philippines are still resistant to BPH 8 . However, the molecular basis of this broad-spectrum and durable resistance of Bph3 against BPH remains unknown.We observed that Bph3-containing Rathu Heenati infested with BPH of mixed biotypes (biotype ...
Genes controlling hormone levels have been used to increase grain yields in wheat (Triticum aestivum) and rice (Oryza sativa). We created transgenic rice plants expressing maize (Zea mays), rice, or Arabidopsis thaliana genes encoding sterol C-22 hydroxylases that control brassinosteroid (BR) hormone levels using a promoter that is active in only the stems, leaves, and roots. The transgenic plants produced more tillers and more seed than wild-type plants. The seed were heavier as well, especially the seed at the bases of the spikes that fill the least. These phenotypic changes brought about 15 to 44% increases in grain yield per plant relative to wild-type plants in greenhouse and field trials. Expression of the Arabidopsis C-22 hydroxylase in the embryos or endosperms themselves had no apparent effect on seed weight. These results suggested that BRs stimulate the flow of assimilate from the source to the sink. Microarray and photosynthesis analysis of transgenic plants revealed evidence of enhanced CO 2 assimilation, enlarged glucose pools in the flag leaves, and increased assimilation of glucose to starch in the seed. These results further suggested that BRs stimulate the flow of assimilate. Plants have not been bred directly for seed filling traits, suggesting that genes that control seed filling could be used to further increase grain yield in crop plants.
Genome editing technologies enable precise modifications of DNA sequences in vivo and offer great promise for crop improvement. CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-associated Cas9) has revolution-
Indole-3-acetic acid (IAA), the natural auxin in plants, regulates many aspects of plant growth and development. Extensive analyses have elucidated the components of auxin biosynthesis, transport, and signaling, but the physiological roles and molecular mechanisms of auxin degradation remain elusive. Here, we demonstrate that the dioxygenase for auxin oxidation (DAO) gene, encoding a putative 2-oxoglutarate-dependent-Fe (II) dioxygenase, is essential for anther dehiscence, pollen fertility, and seed initiation in rice. Rice mutant lines lacking a functional DAO display increased levels of free IAA in anthers and ovaries. Furthermore, exogenous application of IAA or overexpression of the auxin biosynthesis gene OsYUCCA1 phenocopies the dao mutants. We show that recombinant DAO converts the active IAA into biologically inactive 2-oxoindole-3-acetic acid (OxIAA) in vitro. Collectively, these data support a key role of DAO in auxin catabolism and maintenance of auxin homeostasis central to plant reproductive development.
Land plants have evolved increasingly complex regulatory modes of their flowering time (or heading date in crops). Rice (Oryza sativa L.) is a short-day plant that flowers more rapidly in short-day but delays under long-day conditions. Previous studies have shown that the CO-FT module initially identified in long-day plants (Arabidopsis) is evolutionary conserved in short-day plants (Hd1-Hd3a in rice). However, in rice, there is a unique Ehd1-dependent flowering pathway that is Hd1-independent. Here, we report isolation and characterization of a positive regulator of Ehd1, Early heading date 4 (Ehd4). ehd4 mutants showed a never flowering phenotype under natural long-day conditions. Map-based cloning revealed that Ehd4 encodes a novel CCCH-type zinc finger protein, which is localized to the nucleus and is able to bind to nucleic acids in vitro and transactivate transcription in yeast, suggesting that it likely functions as a transcriptional regulator. Ehd4 expression is most active in young leaves with a diurnal expression pattern similar to that of Ehd1 under both short-day and long-day conditions. We show that Ehd4 up-regulates the expression of the “florigen” genes Hd3a and RFT1 through Ehd1, but it acts independently of other known Ehd1 regulators. Strikingly, Ehd4 is highly conserved in the Oryza genus including wild and cultivated rice, but has no homologs in other species, suggesting that Ehd4 is originated along with the diversification of the Oryza genus from the grass family during evolution. We conclude that Ehd4 is a novel Oryza-genus-specific regulator of Ehd1, and it plays an essential role in photoperiodic control of flowering time in rice.
The GCN4 motif, a cis-element that is highly conserved in the promoters of cereal seed storage protein genes, plays a central role in controlling endospermspecific expression. This motif is the recognition site for a basic leucine zipper transcriptional factor that belongs to the group of maize Opaque-2 (O2)-like proteins. Five different basic leucine zipper cDNA clones, designated RISBZ1-5, have been isolated from a rice seed cDNA library. The predicted gene products can be divided into two groups based on their amino acid sequences. Although all the RISBZ proteins are able to interact with the GCN4 motif, only RISBZ1 is capable of activating (more than 100-fold expression) the expression of a reporter gene under a minimal promoter fused to a pentamer of the GCN4 motif. Loss-of-function and gain-of-function experiments using the yeast GAL4 DNA binding domain revealed that the proline-rich N-terminal domain (27 amino acids in length) is responsible for transactivation. The RISBZ1 protein is capable of forming homodimers as well as heterodimers with other RISBZ subunit proteins. RISBZ1 gene expression is restricted to the seed, where it precedes the expression of storage protein genes. When the RISBZ1 promoter was transcriptionally fused to the -glucuronidase reporter gene and the chimeric gene was introduced into rice, the -glucuronidase gene is specifically expressed in aleurone and subaleurone layer of the developing endosperm. These findings suggest that the specific expression of transcriptional activator RISBZ1 gene may determine the endosperm specificity of the storage protein genes.Regulated gene expression is mediated by the combinatorial interactions of multiple cis-elements in the gene's promoter. Specific binding of transcriptional factors to the cognate ciselements constitute a crucial step in transcription initiation and, in turn, on the spatial and temporal expression of genes.Seed storage protein genes provide a model system for the study on the regulatory mechanisms of plant genes (1), since their expression is restricted to a specific tissue and stage during seed development. These specific temporal and spatial expression patterns may be explained as the result of regulatory assemblies of several transcriptional activators that recognize the cis-elements implicated in seed-specific expression. Therefore, to understand such molecular mechanisms, characterization of cis-elements and transcription factors has been performed on many storage protein genes of several crop plants (2,3). Despite numerous studies, the mechanism by which these genes are regulated are poorly understood, since many of the essential cis-elements have not been identified. This is especially true in the case of monocot plants, where many of the promoter analyses of cereal storage protein genes have carried out by transient assays using particle bombardment or heterologous transgenic tobacco system (4 -6). Dissection analyses of promoter using homologous stable transgenic plant have been carried out only on glutelin genes of ...
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