ARCHITECTURE OF FLORAL BRANCH SYSTEMS IN MAIZE AND RELATED GRASSES

Authors: VOLLBRECHT, ERIK - IOWA STATE UNIVERSITY; SPRINGER, PATRICIA - UNIVERSITY OF CALIFORNIA; GOH, LINDEE - COLD SPRING HARBOR LAB; Buckler, Edward - Ed; MARTIENSSEN, ROBERT - COLD SPRING HARBOR LAB

Submitted to: Nature
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/21/2005
Publication Date: 11/11/2005
Citation: Vollbrecht, E., Springer, P.S., Goh, L., Buckler Iv, E.S., Martienssen, R. 2005. Architecture of floral branch systems in maize and related grasses. Nature. 436:1119-1126.

Interpretive Summary: In plant biology, the arrangement of flowers on a stalk is called an inflorescence. Maize is unique to the plant kingdom in having a largely unbranched inflorescence, giving rise to the familiar corncob. As the presence or absence of long branches dictates both fundamental plant architecture and the capacity for flower production, branch length in grasses—including the domesticated cereals—greatly impacts grain-bearing capacity. In this study, we investigated the role of a particular gene, ramosa1, in the evolution of grass inflorescence development by isolating the gene from maize, and subsequently the corresponding gene from several close relatives. This analysis sheds light on potential targets of gene selection during maize domestication, as well as provides steps towards harnessing these targets for future molecular breeding, crop modification and improvement.

Technical Abstract: The external appearance of flowering plants is determined to a large extent by the forms of flower-bearing branch systems, known as inflorescences, and their position in the overall structure of the plant. Branches and branching patterns are produced by tissues called shoot apical meristems. Thus, inflorescence architecture reflects meristem number, arrangement and activity, and the duration of meristem activity correlates with branch length. The inflorescences of maize, unlike those of related grasses such as rice and sorghum, predominantly lack long branches, giving rise to the tassel and familiar corncob. Here we report the isolation of the maize ramosa1 gene and show that it controls inflorescence architecture. Through its expression in a boundary domain near the nascent meristem base, ramosa1 imposes short branch identity as branch meristems are initiated. A second gene, ramosa2, acts through ramosa1 by regulating ramosa1 gene expression levels. Ramosa1 encodes a transcription factor that appears to be absent in rice, is heterochronically expressed in sorghum, and may have played an important role in maize domestication and grass evolution.