Analysis of expressed sequence tags in apomictic guineagrass (Panicum maximum)

Apomixis is an intriguing asexual mode of reproduction, because it produces maternal clones that permit vegetative reproduction through seeds. Guineagrass (Panicum maximum) has both facultative aposporous apomixis and obligate sexual modes of reproduction. Despite the importance of apomixis in guineagrass, expressed sequence tags (ESTs) for this condition have not been studied in this species. We constructed a guineagrass cDNA library from two aposporous strains, Ku5954 and GM64-3A, and utilized them as microarray probes. To find genes uniquely expressed in the immature pistils of apomicts, we performed a microarray analysis using target RNA from another apomict, OKI64. Of the 4608 probes in the microarray, only 394 showed clear gene expression in the immature pistils. Of the 394 expressed probes, 196 were successfully sequenced. Of these, 181 had significant homology with other species, including 10 ESTs with matches in a pistil cDNA library from another aposporous species, Cenchrus ciliaris. Of the remaining ESTs, three showed significant homology only with animal database sequences and the other 12 ESTs showed no homology with any previously registered sequence. In reverse-transcriptase PCR and real-time quantitative PCR, nine ESTs reliably detected ovary-specific gene expression. Of these, three revealed aposporous ovary-specific genes expressed in the early developmental stage, suggesting that these could be apomixis-related genes.