title: Rice Leaf Angle and Grain Size Are Affected by the OsBUL1 Transcriptional Activator Complex.
abstract: Rice atypical HLH protein Oryza sativa BRASSINOSTEROID UPREGULATED 1-LIKE1 (OsBUL1) is preferentially expressed in the lamina joint where it controls cell elongation and positively affects leaf angles. OsBUL1 knockout mutant (osbul1) and transgenic rice for double-stranded RNA interference (dsRNAi) of OsBUL1 produced erect leaves with smaller grains, whereas OsBUL1 overexpressors and an activation tagging line of OsBUL1 exhibited increased lamina inclination and grain size. Moreover, OsBUL1 expression was induced by brassinolide (BL) and osbul1 did not respond to BL treatment. To understand the molecular network of OsBUL1 function in rice, we isolated a novel OsBUL1-interacting protein, LO9-177, an uncharacterized protein containing a KxDL motif, and functionally studied it with respect to the lamina inclination and grain size of rice. OsBUL1 COMPLEX1 (OsBC1) is a basic helix-loop-helix (bHLH) transcriptional activator that interacts with OsBUL1 only in the presence of LO9-177 forming a possible trimeric complex for cell elongation in the lamina joint of rice. Expression of OsBC1 is also upregulated by BL and has a similar pattern to that of OsBUL1 Transgenic rice plants expressing OsBC1 under the control of OsBUL1 promoter showed increased grain size as well as leaf bending, while transgenic lines for dsRNAi and/or expressing a dominant repressor form of OsBC1 displayed reduced plant height and grain size. Together, these results demonstrated that a novel protein complex consisting of OsBUL1, LO9-177, and OsBC1 is associated with the HLH-bHLH system, providing new insight into the molecular functional network based on HLH-bHLH proteins for cell elongation.
authors.affiliation: Biotechnology Center in Southern Taiwan, Tainan 74145/Agricultural Biotechnology Research Center, Academia Sinica, Nankang, Taipei 11529, Taiwan (S.J., H.-Y.L.); florigen@gate.sinica.edu.tw.|Institute of Tropical Plant Science, National Cheng Kung University, Tainan 70101, Taiwan (S.J.); and florigen@gate.sinica.edu.tw.|Crop Biotech Institute, Kyung Hee University, Yongin 17102, Korea (G.A.) florigen@gate.sinica.edu.tw.
authors.forename: Seonghoe
authors.identifier: 0000-0001-5018-3480
authors.initials: S
authors.lastname: Jang
authors.affiliation: Biotechnology Center in Southern Taiwan, Tainan 74145/Agricultural Biotechnology Research Center, Academia Sinica, Nankang, Taipei 11529, Taiwan (S.J., H.-Y.L.).|Institute of Tropical Plant Science, National Cheng Kung University, Tainan 70101, Taiwan (S.J.); and.|Crop Biotech Institute, Kyung Hee University, Yongin 17102, Korea (G.A.).
authors.forename: Gynheung
authors.initials: G
authors.lastname: An
authors.affiliation: Biotechnology Center in Southern Taiwan, Tainan 74145/Agricultural Biotechnology Research Center, Academia Sinica, Nankang, Taipei 11529, Taiwan (S.J., H.-Y.L.).|Institute of Tropical Plant Science, National Cheng Kung University, Tainan 70101, Taiwan (S.J.); and.|Crop Biotech Institute, Kyung Hee University, Yongin 17102, Korea (G.A.).
authors.forename: Hsing-Yi
authors.initials: HY
authors.lastname: Li
mesh_terms: D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism; D060406:Brassinosteroids / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D055786:Gene Knockout Techniques; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism; D012275:Oryza / Q000502:physiology*; D018515:Plant Leaves / Q000033:anatomy & histology* / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic; D012639:Seeds / Q000235:genetics / Q000502:physiology*; D015398:Signal Transduction; D013260:Steroids, Heterocyclic / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D060406:Brassinosteroids; D046912:Multiprotein Complexes; D010940:Plant Proteins; D013260:Steroids, Heterocyclic; D015534:Trans-Activators; C023623:brassinolide