Expression of the H+-ATPase AHA10 proton pump is associated with citric acid accumulation in lemon juice sac cells
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The sour taste of lemons (Citrus limon (L.) Burm.) is determined by the amount of citric acid in vacuoles of juice sac cells. Faris is a “sweet” lemon variety since it accumulates low levels of citric acid. The University of California Riverside Citrus Variety Collection includes a Faris tree that produces sweet (Faris non-acid; FNA) and sour fruit (Faris acid; FA) on different branches; it is apparently a graft chimera with layer L1 derived from Millsweet limetta and layer L2 from a standard lemon. The transcription profiles of Faris sweet lemon were compared with Faris acid lemon and Frost Lisbon (L), which is a standard sour lemon genetically indistinguishable from Faris in prior work with SSR markers. Analysis of microarray data revealed that the transcriptomes of the two sour lemon genotypes were nearly identical. In contrast, the transcriptome of Faris sweet lemon was very different from those of both sour lemons. Among about 1,000 FNA-specific, presumably pH-related genes, the homolog of Arabidopsis H+-ATPase proton pump AHA10 was not expressed in FNA, but highly expressed in FA and L. Since Arabidopsis AHA10 is involved in biosynthesis and acidification of vacuoles, the lack of expression of the AHA10 citrus homolog represents a very conspicuous molecular feature of the FNA sweet phenotype. In addition, high expression of several 2-oxoglutarate degradation-related genes in FNA suggests activation of the GABA shunt and degradation of valine and tyrosine as components of the mechanism that reduces the level of citric acid in sweet lemon.
KeywordsCitrus Microarray Acidity/sourness Proton pump
The authors would like to thank Ottilia Bier for bringing to our attention the presence of sour fruit on the Faris lemon trees, Ray Fenton for isolating the RNA, Jan Svensson for cooperation on identification of reference transcripts, and Barbara Walter for labeling the RNA and processing the gene chips. Avi Sadka provided helpful advice and comments on the results.
- Aprile A, Federici C, Close T, De Bellis L, Cattivelli L, Roose M (2011) High and low acid lemons: origin and transcriptome comparisons. Acta Hort 892:37–42Google Scholar
- Baxter IR, Young JC, Armstrong G, Foster N, Bogenschutz N, Cordova T, Peer WA, Hazen SP, Murphy AS, Harper JF (2005) A plasma membrane H-ATPase is required for the formation of proanthocyanidins in the seed coat endothelium of Arabidopsis thaliana. Proc Natl Acad Sci U S A 102:2649–2654PubMedCrossRefGoogle Scholar
- Benjamini Y, Hochberg Y (1995) Controlling the false discovery rate: a practical and powerful approach to multiple testing. J R Stat Soc 57:289–300Google Scholar
- Bogin E, Wallace A (1966) Organic acid synthesis and accumulation in sweet and sour lemon fruit. J Amer Soc Hort Sci 89:182–194Google Scholar
- Canel C, Bailey-Serres JN, Roose ML (1995) In vitro [14C] citrate uptake by tonoplast vesicles of acidless citrus juice cells. J Amer Soc Hort Sci 120:510–514Google Scholar
- Chapot H (1964) Citrons doux… ou acides? Cah Rech Agron 18:105–112Google Scholar
- Gulsen O, Roose M (2001) Lemons: diversity and relationships with selected citrus genotypes as measured with nuclear genome markers. J Amer Soc Hort Sci 126:309–317Google Scholar
- Irizarry RA, Gautier L, Bolstad BM, Miller C with contributions from Astrand M, Cope LM, Gentleman R, Gentry J, Halling C, Huber W, MacDonald J, Rubinstein BIP, Workman C and Zhang J (2006) Affy: methods for affymetrix oligonucleotide arrays. R package version 1.12.1Google Scholar
- Sadka A, Dahan E, Or E, Roose ML, Marsh KB, Cohen L (2001) Comparative analysis of citrate synthase gene structure, transcript level and enzymatic activity in acidless and acid-containing citrus varieties. Austral J Plant Physiol 28:383–390Google Scholar
- Ting SV, Attaway JA (1971) Citrus fruits. In: Hulme AC (ed) The biochemistry of fruits and their products, Vol. 2. Academic, London, pp 107–169Google Scholar