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A Novel Embryo Phenotype Associated With Interspecific Hybrid Weakness in Rice Is Controlled by the MADS-Domain Transcription Factor OsMADS8.

ABSTRACT: A novel hybrid weakness gene, DTE9, associated with a dark tip embryo (DTE) trait, was observed in CR6078, an introgression line derived from a cross between the Oryza sativa spp. japonica "Hwayeong" (HY) and the wild relative Oryza rufipogon. CR6078 seeds exhibit protruding embryos and flowers have altered inner floral organs. DTE9 was also associated with several hybrid weakness symptoms including decreased grain weight. Map-based cloning and transgenic approaches revealed that DTE9 is an allele of OsMADS8, a MADS-domain transcription factor. Genetic analysis indicated that two recessive complementary genes were responsible for the expression of the DTE trait. No sequence differences were observed between the two parental lines in the OsMADS8 coding region; however, numerous single nucleotide polymorphisms were detected in the promoter and intronic regions. We generated overexpression (OX) and RNA interference (RNAi) transgenic lines of OsMADS8 in HY and CR6078, respectively. The OsMADS8-OX lines showed the dark tip embryo phenotype, whereas OsMADS8-RNAi recovered the normal embryo phenotype. Changes in gene expression, including of ABCDE floral homeotic genes, were observed in the OsMADS8-OX and OsMADS8-RNAi lines. Overexpression of OsMADS8 led to decreased expression of OsEMF2b and ABA signaling-related genes including OsVP1/ABI3. HY seeds showed higher ABA content than CR6078 seeds, consistent with OsMADS8/DTE9 regulating the expression of genes related ABA catabolism in CR6078. Our results suggest that OsMADS8 is critical for floral organ determination and seed germination and that these effects are the result of regulation of the expression of OsEMF2b and its role in ABA signaling and catabolism.

SUBMITTER: Kim SH

PROVIDER: S-EPMC8769243 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Reproductive barriers perform a vital role during speciation1. Hybrid weakness, the poor development of hybrids compared to their parents, hinders gene exchange between different species at the postzygotic stage2,3. The molecular and evolutionary mechanisms of hybrid weakness are poorly understood2. Here, we report that two incompatible dominant loci (Hwi1 and Hwi2) involving three genes determine the high temperature-dependent expression of hybrid weakness in interspecific hybrids of rice. Hwi1 comprises two indispensable wild rice (Oryza rufipogon)-specific leucine-rich repeat receptor-like kinase (LRR-RLK) genes, 25L1 and 25L2, for inducing hybrid weakness, and the genes possibly undergo balancing selection. Hwi2, a rare allele that is predominantly distributed in indica rice (Oryza sativa), encodes a secreted putative subtilisin-like protease. Functional analysis indicated that pyramiding of Hwi1 and Hwi2 activates the autoimmune response in the basal nodes of hybrids, interrupting root formation and then impairing shoot growth, likely due to immune signal is transmitted from the basal nodes to the above-ground parts. Considering the nature of RLK activity of Hwi1 and the protease activity of Hwi2, we propose that a certain endogenous signaling molecule produced by Hwi2 is perceived by Hwi1 to activate autoimmunity through ligand-receptor signal transduction. These findings bring new insights into our understanding of reproductive isolation and may benefit rice breeding to maximally utilize invaluable genes from wild rice. We conducted microarray analysis to unravel the global changes in gene expression of a pair of NILs (nearly isogenic lines). Plants were cultivated at constant 20°C for 20 days and then shifted to constant 30°C conditions. The basal nodes of NIL(Hwi1) and NIL(hwi1) were harvested immediately before the temperature shift (set as the 0 point) or at 3, 7 or 15 days after the shift. Three biological replicates (each comprising basal nodes from 15–20 individuals) were used for each time point.

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A Novel Embryo Phenotype Associated With Interspecific Hybrid Weakness in Rice Is Controlled by the MADS-Domain Transcription Factor OsMADS8.

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