Progress 07/01/08 to 06/30/11
Outputs
OUTPUTS: The long term goal of our research was to understand how a maize leaf is elaborated. The sheath wraps around the stem and the blade tilts back for photosynthesis. At the junction of sheath and blade are the ligule and auricle. Each tissue has unique cell types in specific patterns; for example, the adaxial blade has hairs, while the abaxial sheath has hairs. Ligules form on the adaxial surface and the venation is abaxialized in the sheath. The milkweed pod mutant was our entry point into a genetic analysis of leaf development. We showed that mwp encodes a KANADI like transcription factor. Specific experiments on milkweed pod (mwp) included the analysis of the prophyl, an interesting leaf organ of grasses. The prophyl of mwp mutants end in narrow prongs rather that a bikeeled lamina structure. Our analysis suggests that the HD-ZIP transcription factor, ROLLED, is expressed at a key time in normal development that allows this interesting leaf organ to form. In the mwp mutant background, ROLLED expression is ubiquitous and the lamina fails to form. The data suggest that other unusual leaf structures may arise from regulation of abaxial-adaxial determinants. PARTICIPANTS: Toshi Foster at HortResearch, New Zealand; Brian Dilkes at Purdue, Illinois TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: We moved our attention from mwp to a new mutant that has polarity defects. The dominant mutant, Liguleless narrow (Lgn-R) has hairs on both sides of the leaf blade, rather than only on the adaxial surface. More strikingly are the defects in terms of other axes, proximal-distal and marginal-lateral. The heterozygous leaves are narrow and missing the ligule except at the midrib. The homozygotes are very small and fail to flower. We cloned the gene and found it encodes a serine threonine kinase. The dominant mutant fails to autophosphorylate. A combination of yeast two hybrid assays, RNA analysis and whole mount in situs have helped us place lgn in a pathway with liguleless1 and liguleless2. Lgn is very inbred dependent - the heterozygous phenotype disappears in Mo17, while it is very severe in B73. We crossed Lgn to the IBM (Intermated B73 Mo17) recombinant inbred population to map the modifiers. In a collaboration with Rocheford at Purdue we identified a single Mo17 modifier of strong effect on chromosome 1. Further analysis of the data by Brian Dilkes identified a case of epistasis with a second modifier on chromosome 7. Recently, we discovered a new leaf mutant that has similarities to mwp. We have named it raggedleaf2. Like mwp, it has patches of ectopic margins, however, these are on the blade whereas they are on the sheath or husk leaves in mwp mutants. It does not appear to have other abaxial-adaxial defects. We have mapped it to 2.07.
Impacts
Oral Presentations: FASEB invited talk Aug 2009 Howard Hughes sponsored course in Mexico (Nov 2009) workshop participant, Boulder, CO (January 2010) Keystone meeting, Santa Fe (February 2010) Dept seminar, Carnegie, CA (Feb 2010) Dept seminar, Grinnell College (May 2010) Maize Genetics Society Meeting Illinois (2011) (Moon) Postdoctoral and technical personnel trained under this project: Postdoctoral fellow Hector Candela Anton; Graduate student Robyn Johnston (in New Zealand); Graduate student Jihyun Moon
Publications
- Chuck, G., Candela, H., Hake, S. (2009) Big impact by small RNAs in plant development. Curr Opin Plant Biol. 12:81-86.
- Johnston, R., Candela, H., Hake, S. Foster, T. (2010) The maize milkweed pod1 mutant reveals a mechanism to modify organ morphology. Genesis 48:416-423.
- Moon J, Hake S. (2010) How a leaf gets its shape. Curr Opin Plant Biol. 14:24-30.
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Progress 07/01/09 to 06/30/10
Outputs
OUTPUTS: In collaboration with colleagues in New Zealand, we published a paper in Genesis describing the effect of the milkweed pod (mwp) mutation on leaf width and prophyll development. Leaves in the inflorescence, such as glumes, are narrower. The husk leaves and the sheath portion of the leaf are also narrow. The prophyll wraps around both the stem of the plant and the ear. It is a unique organ that has four leaf margins due to fusion of two leaf primordia. Rolled is expressed transiently to create this novel leaf shape in wild-type plants. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
In mwp mutants, the leaves do not fuse and the prophyl is only two narrow prongs. This work shows how regulation of abaxial or adaxial determinants can generate diversity of leaf morphology. The liguleless narrow (lgn) mutation affects proximal distal polarity. Leaves are narrow and the blade/sheath boundary is blurred. We mapped the gene to position and found a mutation in a serine threonine kinase receptor. A wild-type version of the gene autophosphorylates, but the version from the Lgn mutant background does not. Expression levels of a duplicate gene are increased in the mutant background. Lgn heterozygotes have a phenotype in B73 but not in Mo17. We crossed Lgn in the B73 background to the intermated B73 x Mo17 (IBM) recombinant inbred lines and examined these populations in collaboration with Torbert Rocheford at Purdue University. We identified 11 lines that rescued the phenotype, suggesting that they carry Mo17 modifiers that affect the phenotype. We backcrossed these lines to B73 to further map the region. We mapped two narrow leaf mutants to BIN and found they mapped to the same location. One of these has been shown to interact with mwp. We now know that this gene encodes dicer4, a gene important for the production of small interfering RNAs.
Publications
- Johnston, R., Candela, H., Hake, S.C., Foster, T. 2010. The maize milkweed pod1 mutant reveals a mechanism to modify organ morphology. Genesis. Published online 10.1002/dvg.20622.
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Progress 07/01/08 to 06/30/09
Outputs
OUTPUTS: Research is disseminated by giving talks at meetings, such as the FASEB meeting in Vermont, 2008, the ASPB meeting in Mexico, 2008, a course in Irapuato, Mexico, 2008. Research is also disseminated by writing papers. PARTICIPANTS: Participants are undergraduate and graduate students and postdoctoral fellows. Hector Candela - postdoc Jihyun Moon - graduatue student Grace Kayser - undergraduate Collaboration with Dr. Toshi Foster, HortResearch Palmerston North, New Zealand TARGET AUDIENCES: Other ARS and University scientists, maize breeders, maize seed companies PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
We published a paper in the Plant Cell showing that the milkweed pod (mwp) mutation is due to loss of a KANADI transcription factor. In this paper we describe the phenotype, the positional cloning and document the interaction between the HD-ZIP transcription factor, Rolled, and mwp. Rolled promotes adaxial cell fate while mwp promotes abaxial fate. Mwp affects the sheath of the leaf, but when both mutations are present, the defect expands to the blade as well. The results demonstrate that abaxial and adaxial determinants are needed for normal photosynthetic cells as well as vasculature. In collaboration with colleagues at New Zealand, we have submitted a paper that describes how mwp and Rolled regulate development of the prophyll, the first leaf of the maize ear. The prophyll is a unique organ that has four leaf margins due to fusion of two leaf primordia. Rolled is expressed transiently to create this novel leaf shape. In mwp mutants, the leaves do not fuse and the prophyl is only two narrow prongs. This work shows how regulation of abaxial or adaxial determinants can generate diversity of leaf morphology. The liguleless narrow (lgn) mutation affects proximal distal polarity. Leaves are narrow and the blade/sheath boundary is blurred. We mapped the gene to position and found a mutation in a serine threonine kinase receptor. A wild-type version of the gene autophosphorylates, but the version from the Lgn mutant background does not. Lgn was crossed to other maize mutations that affect leaf development. Lgn is enhanced when crossed to liguleless1 and additive with liguleless2. Lgn completely suppresses dominant knotted mutants. We mapped two narrow leaf mutants to BIN and found they mapped to the same location. One of these has been shown to interact with mwp.
Publications
- Candela Anton, H., Hake, S.C. 2008. The art and design of genetic screens: maize. Nature Reviews Genetics 9:192-203.
- Candela Anton, H., Johnston, R., Gerhold, A., Foster, T., Hake, S.C. 2008. The milkweed pod1 Gene Encodes a KANADI Protein That Is Required for Abaxial/Adaxial Patterning in Maize Leaves. The Plant Cell 20:2073-2087.
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