NAIST 奈良先端科学技術大学院大学 バイオサイエンス領域





梅園賞は、梅園基金の設立趣旨に沿って、熱気溢れる時期にバイオサイエンス研究に精進し、バイオサイエンス研究科において優れた研究成果(論文発表)をあげた本学の助教あるいはポスドク研究員の1 名を顕彰するものです。過去において助教あるいはポスドクとして本学に在籍していた方も選考の対象としています。対象者が研究の推進に中心的な役割を果たしたと認められる発表論文(2015年6月1日〜2017年5月31日の期間に査読付き国際学術誌に発表されたもの)の学術的価値とオリジナリティの高さに審査の重点が置かれています。受賞者には表彰状と目録が授与されました。

第14回梅園賞受賞者 平野良憲博士のコメント





The transcriptional regulation in root development by the SHR-SCR heterodimer bound to the BIRD/IDD transcriptional factor

The plant-specific GAI-RGA-and-SCR (GRAS) family proteins are plant-specific key regulators of transcription in diverse processes including root development, gibberellin signal transduction and phytochrome signaling. Two GRAS proteins, SHORT-ROOT (SHR) and SCARECROW (SCR), cooperatively direct asymmetric cell division and the patterning of root cell types by transcriptional control. SHR is a mobile transcription regulator, which is transcribed in the stele, but moves into the adjacent cell layer where SCR sequesters SHR to the nucleus by forming SHR-SCR heterodimer through conserved GRAS domains. Subsequently, the SHR-SCR complex up-regulates various genes including SCR, CYCLIN D6 and BIRD/INDETERMINATE DOMAIN (IDD)s in conjunction with BIRD IDD transcription factors, although precise details of these specific interactions and actions remain unknown.

We have determined the crystal structures of the SHR-SCR binary and JKD/IDD10-SHR-SCR ternary complexes. Each GRAS domain comprises one α/β core subdomain with an α-helical cap that mediates hetero-dimerization by forming an intermolecular helix bundle. We did not find any DNA-binding motifs in our structure of the SHR-SCR complex, which comprises overall negatively-charged surface potentials, which are unfavorable for binding to highly negatively-charged DNA. Moreover, the structure of the JKD-SHR-SCR complex revealed that the α/β core subdomain of SHR forms the BIRD-binding groove, which specifically recognizes the zinc fingers of JKD. Our structural and biochemical analyses indicate that SHR-SCR function as transcription cofactors by binding to the third and fourth ZFs, (ZF3-ZF4) of JKD out of the N-terminal four ZFs (ZF1 to ZF4) via a specific groove in SHR, and that the ZF1-ZF2-ZF3 of JKD in the JKD-SHR-SCR complex is involved in DNA binding. We identified a conserved SHR-binding motif (SHBM) in 13 BIRD/IDD transcription factors which activate respective different genes. Thus, SHR-SCR serves as a “starting switch of transcription network” by working with BIRD/IDDs via SHBM recognition.

Our results establish a structural basis for GRAS-GRAS and GRAS-BIRD interactions and provide valuable clues towards our understanding of these regulators involved in plant-specific signaling networks.