Comparative Transcript Profiling by cDNA-AFLP Reveals Genes Involved in Pollen-pistil Interaction in Clementine

摘要

In contrast to model species, the selfincompatibility phenomenon in citrus has been poorly studied. It is assumed to be gametophytically determined and genetically controlled by the S-locus, which in other species encodes for glycoproteins (SRNases) showing ribonuclease activity. To investigate pollen pistil interaction, pollen tube growth of two Clementine varieties, ' Comune' (self-incompatible) and 'Monreal' (a 'Comune' self-compatible mutation) was analyzed by histological assays in self- and cross pollination conditions. Cross-pollination assays demonstrated that the mutation leading to self-compatibility in ' Monreal' affected the style functions regulating pollen rejection. Similar rates of pollen germination were observed in both genotypes. However, 'Comune' pollen tubes showed altered morphology and arrested growth in the upper style while in ' Monreal' they grew straight toward the ovary. Moreover, to identify genes putatively involved in pollen-pistil interaction and selfincompatibility, a research based on the cDNA-AFLP technique was carried out to compare the transcript profiles of unpollinated and self-pollinated styles and stigmas of the two cultivars. This analysis identified 96 unigenes such as receptor-like kinases, stress-induced genes, transcripts involved in the phenylpropanoid pathway, transcription factors, and genes related to calcium and hormone signaling. Surprisingly, a high percentage of active long terminal repeat (LTR) and non-LTR retrotransposons were identified among the unigenes, indicating their activation in response to pollination and their possible role in the regulation of selfincompatibility genes.