Location: Plant Gene Expression Center2013 Annual Report
1a. Objectives (from AD-416):
1: To map and characterize leaf mutants in maize. [NP 301, C4, PS 4A] 2: To positionally clone genes that regulate plant architecture in maize. [NP 301, C4, PS 4A] 3: To determine the function of genes through transgenic tests. [NP 301, C4, PS 4A]
1b. Approach (from AD-416):
Maize is an important crop as well as a model organism for other cereals such as sorghum, barley, rice and wheat. The large number of genetic mutants, in combination with the ease of obtaining and mapping additional mutants, makes maize an excellent system for determining the function of genes. We propose to identify genes that regulate maize leaf development and shoot architecture. We will carry out mutagenesis with defined inbreds using the chemical mutagen EMS. Mutants will be characterized genetically and histologically. The genes will be mapped to position and cloned. The functions will be determined by expression analysis and further genetics. We already have two mutants at different stages of analysis. The dominant Liguleless narrow mutant has been mapped to position and beginning characterization is under way. The dominant Wavy auricle in blade1 (Wab1) mutant has been localized to a BAC contig. Once we clone Wab1, we will determine the function of the wild-type gene product. In order to follow expression of the genes we clone, we have developed a vector for gene fusions. We are presently testing this vector with the liguleless1 gene. REPLACING 5335-21000-028-00D (09/10).
3. Progress Report:
This project was terminated on July 15, 2013 and replaced by Project 5335-21000-035-00D. Details of progress on milestones relating to analysis of genes that regulate plant architecture can be found in the 2013 Annual Report for Project 5335-21000-035-00D. See new project for additional information. Significant results were generated over the 5 years of the project, the objectives of which fell under National Program 301, Plant Genetic Resources, Genomics and Genetic Improvement. Work on this project focused on addressing Problem 3A – the need for fundamental knowledge of plant biological and molecular processes. Objective 1. We identified a new maize mutation that has pleiotropic developmental defects. The internodes do not expand regularly, leading to a bunching of leaves and a short stature. The ear tips are fasciated and the plants are sterile. This mutation has been mapped to the bottom of chromosome 1. A mapping population has generated roughly 200 mutants that are being scored with markers for recombination events. We have also created mapping populations for a mutation with upright tassel branches and a dominant Tasselseed mutation. Objective 2. During the course of the 5 years, we cloned a number of genes, most recently, we cloned liguleless narrow. Liguleless narrow was shown to encode a kinase. The paralog gene, sister of liguleless narrow (sln), is expressed at very low levels except in the dominant Lgn-R mutant. One hypothesis is that sln levels increase to compensate for the loss of lgn function. We identified insertions in the sln gene that will help us determine its role in the dominant Lgn-R mutant. Objective 3. We showed that Wavy auricle in blade (Wab1) encodes a TCP transcription factor. This TCP gene is misexpressed in leaves of dominant Wab1-R mutants. We determined that liguleless1 is increased in Wab1-R mutants. We obtained an antibody to LG1 and showed that it is expressed in the preligule band in normal plants. In Wab1-R plants, the LG1 expression expands up into the blade as well as appears earlier in development than in non-mutant siblings. Wab is normally not expressed in leaves, but is expressed in tassels by RNAseq data. Using the LG1 antibody, we found that LG1 is expressed in the axils of tassel branches and that LG1 expression disappears in wab-ref loss of function alleles. Our hypothesis is that WAB is normally expressed in tassels and regulates LG1. In the gain of function mutant, it misexpresses LG1, leading to the dramatic leaf phenotypes. In the wab-ref loss of function allele, lg1 expression disappears and the tassel branches are fewer and more upright.
1. How a genotype interacts with the environment is an important and complex question. The Lgn mutant is sensitive to both background and environment. We cloned Lgn and showed it encodes a kinase. We also mapped a rescuing modifier to a small region. Understanding how the kinase functions and how the modifier rescues the defect may provide critical information for adapting crop plants to harsh environments.