Title

Author

Degree Type

Dissertation

Date of Award

2013

Degree Name

Doctor of Philosophy

Department

Genetics, Development and Cell Biology

First Advisor

Erik W. Vollbrecht

Abstract

Inflorescence branch number in maize and other cereal crops has long been recognized as an important factor impacting grain yield. In maize, inflorescence architecture is determined by the collective actions of many genes. Among these, the ramosa mutants play an important role in regulating branch number by imposing short-branch identity on lateral meristems of the inflorescence. In addition, a number of QTL have been identified which alter the branching of male inflorescences, however few of these QTL co-localize with known inflorescence branching genes, indicating that some components of this pathway have yet to be discovered. We conducted a suppressor/enhancer screen to identify modifiers of the ramosa phenotype and discovered twenty two putative mutants that enhance or suppress the phenotypes of ramosa mutants. Mapping of a portion of these mutants revealed that a subset map to regions of the genome not known to harbor inflorescence genes. As an extension of this method, we performed a screen for natural suppressors and enhancers of the ra1-63.3359 and ra2-R ear branching phenotypes using the intermated B73 Ã? Mo17 (IBM) population of maize. Through this approach we discovered eight QTL that significantly alter the inflorescence branching phenotype of ra1-63.3359 or ra2-R mutants. One of these QTL was present in both the ramosa1 and ramosa2 experiments indicating that it might function directly or in close association with the ramosa pathway. We fine-mapped this region using recombinants derived from a near-isogenic line and narrowed the interval to a region containing nine candidate genes. Ongoing efforts to map the induced mutations or natural variation underlying these ramosa modifiers will help elucidate the processes governing inflorescence architecture.