Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2007
Publication Date: 7/9/2007
Citation: Singh, M., Burson, B.L., Finlayson, S.A. 2007. Isolation of candidate genes for apomictic development in buffelgrass (Pennisetum ciliare). Plant Molecular Biology. 64:673-682. Interpretive Summary: Apomixis is a reproductive process in plants where seed are produced without the union (fertilization) of the egg cell and sperm (gametes) to form an embryo. Thus, it is an asexual or vegetative form of reproduction in which the end product is same as vegetatively cloning or dividing a plant. When the seed that are produced by an apomictic plant are germinated and the seedlings are grown in a field, all offspring look the same (uniform) and are identical to the plant that produced the original seed. There has been a great deal of interest in using apomixis in the development of uniform, true breeding, vigorous hybrids in many of the food and grain crops, but apomixis does not naturally occur in any of these major crops. Efforts to transfer apomixis to these crops from wild relatives using conventional breeding methods have not been successful. Apomixis occurs in many of the warm-season grasses including buffelgrass. In the past, a great deal of research has been conducted studying the genetics of apomixis in this grass, and because of this, buffelgrass is an excellent model species to use in learning more about apomixis. In this study, molecular tools were used to search for genes that are involved in the expression of apomixis. Two genes were identified and it was determined that both were active during the development of reproductive tissue in apomictic buffelgrass. These findings indicate that these genes probably play a role in apomictic development in buffelgrass. Additional research is needed but this may be an important piece of the puzzle of learning what controls apomixis.
Technical Abstract: Asexual reproduction through seeds, or apomixis, is a process that holds much promise for agricultural advances. However, the molecular mechanisms underlying apomixis are currently poorly understood. To identify genes related to female gametophyte development in apomictic ovaries of buffelgrass (Pennisetum ciliare (L.) Link), Suppression Subtractive Hybridization of ovary cDNA with leaf cDNA was performed. Through macroarray screening of subtracted cDNAs, two genes were identified, Pca21 and Pca24, that showed differential expression between apomictic and sexual ovaries. Sequence analysis showed that both Pca21 and Pca24 are novel genes not previously characterized in plants. Pca21 shows homology to two wheat genes that are also expressed during reproductive development. Pca24 has similarity to coiled-coil-helix-coiled-coil-helix (CHCH) domain containing proteins from maize and sugarcane. Northern blot analysis revealed that both of these genes are expressed throughout female gametophyte development in apomictic ovaries. In situ hybridizations localized the transcript of these two genes to the developing embryo sacs in apomictic ovaries. Based on the expression patterns, it was concluded that Pca21 and Pca24 likely play a role during apomictic development in buffelgrass.