2006 Annual Report 4d.Progress report. This report serves to document research conducted under a reimbursable agreement between ARS and CSREES through a National Research Initiative (NRI) grant. Additional details of research can be found in the report for the parent project 5335-21000-018-00D, Isolation and Analysis of Genes that Function in Plant Meristems to Regulate Growth. Research conducted under NRI project 5335-21000-018-03T (which ended 8/14/2005) continues with this NRI-funded project. During this last year, postdoctoral fellow George Chuck, who is a co-PI on the project, cloned the tasselseed4 gene, which functions upstream of branched silkless1 (bd1). He showed it was a microRNA and identified the target genes that it regulates. One of these target genes is indeterminate spikelet1. We also mapped reverse germ orientation (rgo), a mutation that affects the same meristem as bd1. Positional cloning of rgo is in progress. RGO, IDS1 and TS4 are likely to function in the same pathway as BD1. A manuscript describing the cloning of ts4 was submitted to Science. We are carrying out additional experiments and will resubmit this fall. A manuscript describing the target genes of BD1 will be written this fall.