Citrus PH5-like H +-ATPase genes: identification and transcript analysis to investigate their possible relationship with citrate accumulation in fruits

摘要

PH 5 is a petunia gene that encodes a plasma membrane H~(+)-ATPase and determines the vacuolar pH. The citrate content of fruit cell vacuoles influences citrus organoleptic qualities. Although citrus could have PH 5-like homologs that are involved in citrate accumulation, the details are still unknown. In this study, extensive data-mining with the PH 5 sequence and PCR amplification confirmed that there are at least eight PH 5-like genes ( CsPH 1-8) in the citrus genome. CsPHs have a molecular mass of approximately 100 kDa, and they have high similarity to PhPH5, AtAHA10 or AtAHA2 (from 64.6 to 80.9%). They contain 13–21 exons and 12–20 introns and were evenly distributed into four subgroups of the P3A-subfamily ( CsPH 1, CsPH 2, and CsPH 3 in Group I, CsPH 4 and CsPH 5 in Group II, CsPH 6 in Group IV, and CsPH 7 and CsPH 8 in Group III together with PhPH 5). A transcript analysis showed that CsPH 1, 3, and 4 were predominantly expressed in mature leaves, whereas CsPH 2 and 7 were predominantly expressed in roots, CsPH 5 and 6 were predominantly expressed in flowers, and CsPH 8 was predominantly expressed in fruit juice sacs (JS). Moreover, the CsPH transcript profiles differed between orange and pummelo, as well as between high-acid and low-acid cultivars. The low-acid orange “Honganliu” exhibits low transcript levels of CsPH 3, CsPH 4, CsPH 5, and CsPH 8, whereas the acid-free pummelo (AFP) has only a low transcript level of CsPH 8. In addition, ABA injection increased the citrate content significantly, which was accompanied by the obvious induction of CsPH 2, 6, 7, and 8 transcript levels. Taken together, we suggest that CsPH 8 seems likely to regulate citrate accumulation in the citrus fruit vacuole.