AUTHOR=Shi Cai-Yun , Song Rui-Qin , Hu Xiao-Mei , Liu Xiao , Jin Long-Fei , Liu Yong-Zhong 

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

JOURNAL=Frontiers in Plant Science

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2015.00135

DOI=10.3389/fpls.2015.00135

ISSN=1664-462X

ABSTRACT=<p><italic>PH</italic>5 is a petunia gene that encodes a plasma membrane H<sup>+</sup>-ATPase and determines the vacuolar pH. The citrate content of fruit cell vacuoles influences citrus organoleptic qualities. Although citrus could have <italic>PH</italic>5-like homologs that are involved in citrate accumulation, the details are still unknown. In this study, extensive data-mining with the <italic>PH</italic>5 sequence and PCR amplification confirmed that there are at least eight <italic>PH</italic>5-like genes (<italic>CsPH</italic>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 (<italic>CsPH</italic>1, <italic>CsPH</italic>2, and <italic>CsPH</italic>3 in Group I, <italic>CsPH</italic>4 and <italic>CsPH</italic>5 in Group II, <italic>CsPH</italic>6 in Group IV, and <italic>CsPH</italic>7 and <italic>CsPH</italic>8 in Group III together with <italic>PhPH</italic>5). A transcript analysis showed that <italic>CsPH</italic>1, 3, and 4 were predominantly expressed in mature leaves, whereas <italic>CsPH</italic>2 and 7 were predominantly expressed in roots, <italic>CsPH</italic>5 and 6 were predominantly expressed in flowers, and <italic>CsPH</italic>8 was predominantly expressed in fruit juice sacs (JS). Moreover, the <italic>CsPH</italic> 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 <italic>CsPH</italic>3, <italic>CsPH</italic>4, <italic>CsPH</italic>5, and <italic>CsPH</italic>8, whereas the acid-free pummelo (AFP) has only a low transcript level of <italic>CsPH</italic>8. In addition, ABA injection increased the citrate content significantly, which was accompanied by the obvious induction of <italic>CsPH</italic>2, 6, 7, and 8 transcript levels. Taken together, we suggest that <italic>CsPH</italic>8 seems likely to regulate citrate accumulation in the citrus fruit vacuole.</p>