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Comparative transcriptome analysis of stylar canal cells identifies novel candidate genes implicated in the self-incompatibility response of Citrus clementina

DOI: 10.1186/1471-2229-12-20

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Abstract:

The transcriptome profiling of SCC indicated that the differential regulation of few specific, mostly uncharacterized transcripts is associated with the breakdown of self-incompatibility in 'Monreal'. Among them, a novel F-box gene showed a drastic up-regulation both in laser microdissected stylar canal cells and in self-pollinated whole styles with stigmas of 'Comune' in concomitance with the arrest of pollen tube growth. Moreover, we identify a non-characterized gene family as closely associated to the self-incompatibility genetic program activated in 'Comune'. Three different aspartic-acid rich (Asp-rich) protein genes, located in tandem in the clementine genome, were over-represented in the transcriptome of 'Comune'. These genes are tightly linked to a DELLA gene, previously found to be up-regulated in the self-incompatible genotype during pollen-pistil interaction.The highly specific transcriptome survey of the stylar canal cells identified novel genes which have not been previously associated with self-pollen rejection in citrus and in other plant species. Bioinformatic and transcriptional analyses suggested that the mutation leading to self-compatibility in 'Monreal' affected the expression of non-homologous genes located in a restricted genome region. Also, we hypothesize that the Asp-rich protein genes may act as Ca2+ "entrapping" proteins, potentially regulating Ca2+ homeostasis during self-pollen recognition.Among the citrus species, several pummelos (Citrus grandis L. Osbeck) and mandarin-like varieties are self-incompatible [1]. Clementine mandarin (Citrus clementina Hort. ex Tan.), derived from an uncontrolled cross between a sweet orange and a mandarin, is probably the most widespread citrus species showing self-incompatibility (SI). It is characterized by gametophytic SI, with the pollen tubes stopping their growth in the upper or middle style [2,3]. Moreover, in this species SI is coupled with a variable degree of parthenocarpy. SI and parthenocarpy

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