Molecular cloning and characterization of the chloride channel gene family in trifoliate orange

Abstract

Chloride channels (CLCs) play pivotal roles in plant development and anion transport. However, little research has been conducted about the CLC in fruit-bearing plants. Here we provide an insight into the evolution and expression patterns of CLC gene family members in various tissues of trifoliate orange [Poncirus trifoliata (L.) Raf.] and their responses to several treatments. Genome-wide analysis identified six PtrCLC genes. The predicted proteins had similar numbers of amino acids, but shared a low sequence identity. Phylogenetic analysis revealed that PtrCLC were classified into two separate subgroups, and PtrCLC4 and PtrCLC6 in subgroup II were more closely related to bacterial CLCs. Sequence comparison with EcCLCA from Escherichia coli reveals that PtrCLC showed amino acid divergence in anion selectivity of CLC proteins. RT-qPCR analysis shows that PtrCLC genes, particularly PtrCLC6, preferentially expressed in leaves. Nitrogen deficiency irreversibly inhibited expression of PtrCLC genes except for PtrCLC1. In contrast, NaCl stress profoundly induced expression of PtrCLC genes, particularly PtrCLC2 and PtrCLC4, both of which were also upregulated by ABA treatment. The results presented here provide a solid foundation for a future functional research on citrus CLC genes.

Genome-wide identification and expression analysis of the CLC gene family in pomegranate (Punica granatum) reveals its role in salt resistance

“…1). The CLCs topology was consistent with that of Arabidopsis [28,29], tobacco [40], tea (Camellia sinensis) [19] and trifoliate orange [18]. Phylogenetic analysis also indicated multiple rounds of ancient gene expansion (Fig.…”

“…While the accumulation pattern of SO 4 2− was associated with the other genes, such as sulfate transporters [55]. Wei et al [18] found that PtrCLC genes were dramatically induced in response to NaCl stress, and PtrCLC6 showed a leaf-speci c expression pattern in trifoliate orange. Zhang et al [40] observed that all of the expressed NtCLC genes had a low expression level in tobacco roots under salt stress.…”

“…In land plants, the rst CLC gene, CLC-Nt1, was cloned in tobacco [15]. Subsequently, numerous CLC gene homologues were isolated from Arabidopsis [16], rice (Oryza sativa) [17], soybean and trifoliate orange (Poncirus trifoliata) [18], etc. All of the CLC proteins have a highly conserved voltage-gated chloride channel (Voltage-gate CLC) domain and two CBS (cystathionine beta synthase)…”

“…In other plants, many CLC genes are involved in anions transport and in the response to salt stress. For instance, the expression level of OsCLC-1 is upregulated in rice under NaCl stress [17]; PtrCLC genes are profoundly induced in orange by salt stress [18]; GmCLC1 has been found to enhanced salt tolerance in transgenic Arabidopsis seedlings by reducing the Cl − accumulation in shoots [6]; and GsCLC-c2 over-expression contributes to Cl − and NO 3 − homeostasis, and therefore confers wild soybean the salt tolerance [32].…”

Chloride on the Move

“…Tonoplast AtCLCc secretes Clinto root vacuoles and helps improve salt tolerance, and regulates gas exchange through its role in light induced opening and ABA-induced closure [74]; AtCLCg, localized to mesophyll tonoplast, is predicted to have a similar role for Clcompartmentation in leaf mesophyll as its knockout showed increased sensitivity to salt [75]. CLC have their expression upregulated by salt in rice, maize and citrus [80][81][82], and overexpression of tonoplast localized GmCLC1 in soybean increased its salt tolerance [83,84], indicating, again that direct transfer of Clis not the only factor controlling Cl --related tolerance in plants. For further information on other CLC members, which also localize to other endo-membrane, we refer readers to [85].…”