Abstract
Self-incompatibility (SI) is one of the important factors that can result in seedless fruit in Citrus. However, the molecular mechanism of SI in Citrus is not yet clear. In this study, two suppression subtractive hybridization (SSH) libraries (forward, F and reverse, R) were constructed to isolate differentially expressed genes in pollen from “Wuzishatangju” (SI) and “Shatangju” (self-compatibility, SC) mandarins. Four hundred and sixty-eight differentially expressed cDNA clones from 2077 positive clones were sequenced and identified. Differentially expressed ESTs are possibly involved in the SI reaction of “Wuzishatangju” by regulating pollen development, kinase activity, ubiquitin pathway, pollen-pistil interaction, and calcium ion binding. Twenty five SI candidate genes were obtained, six of which displayed specific expression patterns in various organs and stages after self- and cross-pollination. The expression level of the F-box gene (H304) and S1 (F78) in the pollen of “Wuzishatangju” was 5-fold higher than that in “Shatangju” pollen. The F-box gene, S1, UBE2, UBE3, RNaseHII, and PCP were obviously up-regulated in pistils at 3 d after self-pollination of “Wuzishatangju”, approximately 3-, 2-, 10-, 5-, 5-, and 2-fold higher, respectively than that at the same stage after cross-pollination of “Wuzishatangju” × “Shatangju” pistils. The potential involvement of these genes in the pollen SI reaction of “Wuzishatangju” is discussed.
Highlights
IntroductionSelf-incompatibility (SI) is a widespread mechanism in angiosperms which allows the pistil of a flower to reject self (genetically related) pollen, but to accept non-self (genetically unrelated) pollen for fertilization [1]
Self-incompatibility (SI) is a widespread mechanism in angiosperms which allows the pistil of a flower to reject self pollen, but to accept non-self pollen for fertilization [1]
In 2000, a cDNA fragment of the pollen S gene was first identified from Nicotiana alata and it was primarily expressed during pollen development [10]
Summary
Self-incompatibility (SI) is a widespread mechanism in angiosperms which allows the pistil of a flower to reject self (genetically related) pollen, but to accept non-self (genetically unrelated) pollen for fertilization [1]. In the SSI system of Brassicaceae, growth of the pollen tube arrests at the surface of the stigma and a kinase-mediated signaling cascade is involved in the SI reaction [2]. In the GSI system of Rosaceae, Solanaceae, and Plantaginaceae, the arrest of growth of incompatible pollen tubes is in styles and its SI reaction is genetically controlled by style-expressed S-RNase (S locus-encoded Ribonuclease) genes [3]. Pollen-expressed SFB (S-haplotype-specific F-box)/SLF (S-locus F-box) genes [4,5,6]. Style-expressed S-RNase genes have been isolated from the Solanaceae [7], Rosaceae [8], and Plantaginaceae [9]. AhSLF-S2 (Antirrhinum hispanicum S-locus F-box of S2-haplotype), a candidate pollen S-determinant gene [4], and PiSLF2 (S2-allele of Petunia inflata S-locus F-box) [11]
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