AUTHOR=Kim Sun Ha , Ji Shi-Dong , Lee Hyun-Sook , Jeon Yun-A , Shim Kyu-Chan , Adeva Cheryl , Luong Ngoc Ha , Yuan Pingrong , Kim Hyun-Jung , Tai Thomas H. , Ahn Sang-Nag 

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

JOURNAL=Frontiers in Plant Science

VOLUME=12

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.778008

DOI=10.3389/fpls.2021.778008

ISSN=1664-462X

ABSTRACT=<p>A novel hybrid weakness gene, <italic>DTE9</italic>, associated with a dark tip embryo (DTE) trait, was observed in CR6078, an introgression line derived from a cross between the <italic>Oryza sativa</italic> spp. <italic>japonica</italic> “Hwayeong” (HY) and the wild relative <italic>Oryza rufipogon</italic>. CR6078 seeds exhibit protruding embryos and flowers have altered inner floral organs. <italic>DTE9</italic> was also associated with several hybrid weakness symptoms including decreased grain weight. Map-based cloning and transgenic approaches revealed that <italic>DTE9</italic> is an allele of <italic>OsMADS8</italic>, 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 <italic>OsMADS8</italic> 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 <italic>OsMADS8</italic> in HY and CR6078, respectively. The <italic>OsMADS8-</italic>OX lines showed the dark tip embryo phenotype, whereas <italic>OsMADS8</italic>-RNAi recovered the normal embryo phenotype. Changes in gene expression, including of ABCDE floral homeotic genes, were observed in the <italic>OsMADS8</italic>-OX and <italic>OsMADS8</italic>-RNAi lines. Overexpression of <italic>OsMADS8</italic> led to decreased expression of <italic>OsEMF2b</italic> and ABA signaling-related genes including <italic>OsVP1/ABI3</italic>. HY seeds showed higher ABA content than CR6078 seeds, consistent with <italic>OsMADS8/DTE9</italic> regulating the expression of genes related ABA catabolism in CR6078. Our results suggest that <italic>OsMADS8</italic> is critical for floral organ determination and seed germination and that these effects are the result of regulation of the expression of <italic>OsEMF2b</italic> and its role in ABA signaling and catabolism.</p>