Scanning electron micrograph of an abphyl1 mutant vegetative shoot meristem.  Leaf primordia are labeled 2,3.

Scanning electron micrograph of an abphyl1 mutant vegetative shoot meristem. Leaf primordia are labeled 2,3.

This project is funded by NIFA.

The abphyl1 mutation affects the geometric pattern of leaf initiation, leading to plants with opposite leaf arrangements instead of the usual alternating pattern found in maize. This pattern starts in the embryo, where the shoot apical meristem is enlarged. We have isolated new alleles of abph1 using Mutator and Spm transposon tagging, and used them to isolate ABPH1. The way in which leaf arrangements are determined is not well understood, so this gene should provide a unique insight into this classical biological question.

A scanning electron micrograph of a vegetative maize shoot meristem.

A scanning electron micrograph of a vegetative maize shoot meristem.

Normal and abphyl1 maize plants. The abphyl1 mutant is on the right, and makes leaves and ears in opposite pairs.

Normal and abphyl1 maize plants. The abphyl1 mutant is on the right, and makes leaves and ears in opposite pairs.

Recent studies have focused on a similar phyllotaxy mutant, Abph2, which is caused by a dominant mutation. Mapping brought Abph2 into a region of ~ 20kb on chromosome 7, containing 5 predicted genes. However, direct sequencing of their open reading frames, as well as their transcript analysis, did not give any obvious clues as to the identity of theAbph2 gene. Therefore, a BAC library generated from the Abph2 mutant was screened, and revealed a 4.5kb fragment inserted into the 20kb mapping interval. This inserted fragment contained a transposed gene identical to one located about 800kb upstream. A transformed maize line containing this 4.5kb fragment fused with YFP tag phenocopied the dominantAbph2 phyllotaxy defect, demonstrating the inserted gene is the cause for the phyllotaxy phenotype. Current work is focused on understanding the role of this gene in meristem development.