INVESTIGATOR: Schnable, P. S.

PERFORMING INSTITUTION:
AGRONOMY
IOWA STATE UNIVERSITY
AMES, IOWA 50011

ROLE OF ALDEHYDE DEHYDROGENASE ACTIVITY IN MALE FERTILITY OF MAIZE

OBJECTIVES: 9801805. The physiologically significant aldehyde substrate(s) upon which the rf2-encoded aldehyde dehydrogenase acts during the process of male fertility restoration in T-cytoplasm maize will be detty restoration in T-cytoplasm maize will be determined. In parallel, the function of the newly identified pif1 gene, that in combination with rf2 mutants conditions male sterility in normal cytoplasm maize, will be determined at the phenotypic level.

APPROACH: Kinetic studies will be conducted on a collection of aldehyde dehydrogenase enzymes. To accomplish this, full-length cDNA clones will be isolated for each enzyme and expressed in E. coli. Using the resulting E. coli strains, the preferred substrates will be determined for each enzyme. The resulting information will be used to select aldehyde dehydrogenase genes that will be used in transgenic maize experiments designed to determine functionally significant aldehyde substrate of the rf2 gene. The morphological changes in anther development associated with a mutant allele of the pif1 gene will be determined via microscopic examination. The ability of the pif1 gene to function as a nuclear restorer of T-cytoplasm maize will be tested via genetic crosses.

PROGRESS: 1999/01 TO 1999/12
The rf2a gene encodes an aldehyde dehydrogenase (ALDH) that is required for male fertility. However, the physiologically significant substrate of this enzyme is not known. Identifying this substrate represents a central focus of research. One possible substrate is the acetaldehyde produced during fermentation. The fermentation pathway involves at least entation pathway involves at least two proteins in addition to ALDH: alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC). A genetic approach is being utilized to test the hypothesis that ethanolic fermentation is involved in male fertility in maize. Specifically, experiments are being conducted to determine whether knock-out mutants of genes that code for enzymes in this pathway (ADH, and PDC) condition male sterility (as do mutants of the rf2a gene). In maize, ADH and PDC are encoded by two and three genes, respectively. Previously it was established that adh1 or adh2 mutants do not cause male sterility in T-cytoplams maize and that these mutants do not interact genetically with an rf2a mutant. Because mutants in the pdc genes were not available, a reverse genetic screen is being utilized to isolate Mu transposon insertion mutants in each of the three PDC-encoding (pdc1, pdc2 and pdc3) of maize. To design such knock-out experiments in maize it is necessary to obtain gene structures and genetic map positions for each gene. Genomic clones have been isolated and sequenced for each of the PDC-encoding genes. Mu insertions have been obtained in each of the three PDC-encoding genes. The two pdc1 alleles have Mu insertions 5' of the coding region, and the pdc2 and pdc3 alleles have exonic Mu transposons insertions. No evidence has been obtained for a genetic interaction between rf2a and pdc3. The pdc3 mutations are and pdc3. The pdc3 mutations are the first mutants in a PDC-encoding gene to be isolated from any species. As such they represented a unique resource for testing the hypothesis that the PDC protein plays an important role in resistance to anaerobic stress. Although, pdc3 mutants also do not condition male sterility, they do confer substantially reduced seedling resistance to hypoxic conditions.

IMPACT: 1999/01 TO 1999/12
This research is developing strategies to address the challenges biologists will face in the "post- post-genomic" era when most genes will have been cloned, sequenced and their biochemical functions known.

PUBLICATIONS: 1999/01 TO 1999/12
No publications reported this period

PROJ. CONTACT:

Name: Good, C.
Phone: 515-294-4544
Fax: 515-294-2909
Email: cgood@iastate.edu