Abstract
PH5 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 PH5-like homologs that are involved in citrate accumulation, the details are still unknown. In this study, extensive data-mining with the PH5 sequence and PCR amplification confirmed that there are at least eight PH5-like genes (CsPH1-8) 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 (CsPH1, CsPH2, and CsPH3 in Group I, CsPH4 and CsPH5 in Group II, CsPH6 in Group IV, and CsPH7 and CsPH8 in Group III together with PhPH5). A transcript analysis showed that CsPH1, 3, and 4 were predominantly expressed in mature leaves, whereas CsPH2 and 7 were predominantly expressed in roots, CsPH5 and 6 were predominantly expressed in flowers, and CsPH8 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 CsPH3, CsPH4, CsPH5, and CsPH8, whereas the acid-free pummelo (AFP) has only a low transcript level of CsPH8. In addition, ABA injection increased the citrate content significantly, which was accompanied by the obvious induction of CsPH2, 6, 7, and 8 transcript levels. Taken together, we suggest that CsPH8 seems likely to regulate citrate accumulation in the citrus fruit vacuole.
Highlights
PH5 is a petunia gene that encodes a plasma membrane H+-ATPase (P-type ATPase) and has a demonstrated function in determining the vacuolar pH (Verweij et al, 2008; Faraco et al, 2014)
“Anliu” flowers and mature leaves (ML) were collected from “Anliu” trees at the inflorescence stage, fruit juice sacs (JS) were collected from “Anliu” fruits at 123 days after flowering (DAF), and fibrous roots (RT) were harvested from “Anliu” seedlings when the seedling height was over 10 cm
Data Mining, Identification and Molecular Characterization of Citrus PH5-Like H+-ATPase Genes An extensive search was performed in three citrus genome databases using the Petunia PH5 (ABC59935) or Arabidopsis AHA10 (AAB32310) sequence
Summary
PH5 is a petunia gene that encodes a plasma membrane H+-ATPase (P-type ATPase) and has a demonstrated function in determining the vacuolar pH (Verweij et al, 2008; Faraco et al, 2014). P-type ATPases are involved in many physiological functions such as the activation of secondary transport, cellular nutrient uptake, cell expansion, stress adaptation, and plant growth and development (Michelet and Boutry, 1995; Palmgren, 2001; Gaxiola et al, 2007; Duby and Boutry, 2009; Schumacher and Krebs, 2010) They are involved in intracellular pH regulation (Michelet and Boutry, 1995) and have a central role in vacuole acidification (Brune et al, 2002; Verweij et al, 2008; Faraco et al, 2014)
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