Two Genes (ClS1 and ClF-box) Involved the Self-Incompatibility of ”Xiangshui” Lemon (Citrus limon (L.) Burm. f.)

Abstract

Gametophytic self-incompatibility (GSI) is an important factor affecting fruit development and is one of the important mechanisms of seedlessness in citrus. Although many studies have investigated the mechanisms of SI, this process remains unclear in “Xiangshui” lemon (C. limon). In this study, we cloned one S-RNase homologous gene and one SLF homologous gene from the “Xiangshui” lemon, designated as ClS1 (pistil-specific expression) and ClF-box (pollen-specific expression), which contain open reading frames (ORFs) of 534 and 810 bp, respectively. The expression pattern of these two genes was analyzed by quantitative real-time polymerase chain reaction, and the results showed that the expression pattern of these two genes was significantly upregulated after self-pollination compared to that after cross-pollination. Through pollination in transgenic tobacco, we found that the pollen tubes grew slowly and became twisted after cross-pollination of ClS1♀ and ClF-box ♂ transgenic tobaccos, but the pollen tubes of control, self-pollination ClS1 and cross-pollination ClS1♂, and ClF-box ♀ grew normally. Furthermore, significantly fewer pollen tubes of ClS1♀ and ClF-box ♂ entered the ovules than that in other combinations, and the seed number of cross-pollination ClS1♀ and ClF-box ♂ transgenic tobaccos was significantly reduced. These results indicated that the ClS1 and ClF-box genes contribute to the self-incompatibility of the “Xiangshui” lemon.