Brassinosteroids (BRs) are steroid hormones that play essential roles in plant growth and development. We previously cloned qGL3, a major quantitative trait locus regulating grain length in rice (Oryza sativa). The O. sativa japonica var N411 has extra-large grains compared with the O. sativa indica var 9311, and the recessive qgl3 allele from N411 contributes positively to grain length. qGL3 encodes a putative protein phosphatase with Kelch-like repeat domains, an ortholog of Arabidopsis (Arabidopsis thaliana) brassinosteroid-insensitive1 SUPPRESSOR1 (BSU1). BSU1 positively regulates BR signaling, while overexpression of qGL3 induced BR loss-of-function phenotypes. Both qGL3N411 and qGL39311 physically interact with the rice glycogen synthase kinase 3 (GSK3)/SHAGGY-like kinase 3 (OsGSK3), an ortholog of Arabidopsis BR INSENSITIVE2 (BIN2). qGL39311 dephosphorylates OsGSK3, but qGL3N411 lacks this activity. Knocking out OsGSK3 enhances BR signaling and induces nuclear localization of O. sativa BRASSINAZOLE RESISTANT1 (OsBZR1). Unlike the dephosphorylation of BIN2 (which leads to protein degradation) in Arabidopsis, qGL3 dephosphorylates and stabilizes OsGSK3 in rice. These results demonstrate that qGL3 suppresses BR signaling by regulating the phosphorylation and stability of OsGSK3, which modulates OsBZR1 phosphorylation and subcellular distribution. Our study clarifies the role of qGL3 in the regulation of grain length and provides insight into BR signaling, including the differences between rice and Arabidopsis.
油菜素內酯(BRs)是甾體激素，在植物生長發(fā)育過程中起關鍵作用。我們先前克隆了qGL3，一個控制水稻籽粒長度的主效QTL。與秈稻品種93-11相比，粳稻品種N411的籽粒超大，來自N411的隱性等位基因qgl3能增加粒長。qGL3編碼一個帶有Kelch重復域的蛋白磷酸酶，該酶與擬南芥BSU1同源。BSU1正調控BR信號傳導，而過表達qGL3導致了BR功能缺失表型。qGL3N411和qGL39311都能與水稻GSK3/SHAGGY類激酶OsGSK3互作，OsGSK3與擬南芥BIN2同源。qGL39311能去磷酸化OsGSK3，但qGL3N411沒有這個活性。敲除OsGSK3增強了BR信號傳導，造成OsBZR1的核定位。與擬南芥中BIN2去磷酸化后被降解不同，水稻中qGL3去磷酸化OsGSK3并能使其穩(wěn)定。這些結果說明qGL3通過調控OsGSK3的磷酸化和穩(wěn)定性來抑制BR信號傳導，而OsGSK3能控制OsBZR1的磷酸化和亞細胞定位。我們的研究闡明了qGL3對粒長調控所起的作用，深入理解了BR信號傳導機制，包括水稻和擬南芥中的差異。