title: Expression of the H+-ATPase AHA10 proton pump is associated with citric acid accumulation in lemon juice sac cells.
abstract: 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.
authors.affiliation: Department of Biotechnology and Environmental Science, University of Salento, Lecce, Prov.le Lecce-Monteroni, Italy. alessio.aprile@unisalento.it
authors.forename: Alessio
authors.initials: A
authors.lastname: Aprile
authors.forename: Claire
authors.initials: C
authors.lastname: Federici
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Close
authors.forename: Luigi
authors.initials: L
authors.lastname: De Bellis
authors.forename: Luigi
authors.initials: L
authors.lastname: Cattivelli
authors.forename: Mikeal L
authors.initials: ML
authors.lastname: Roose
mesh_terms: D019343:Citric Acid / Q000378:metabolism*; D002957:Citrus / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D016000:Cluster Analysis; D005638:Fruit / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D020869:Gene Expression Profiling; D006863:Hydrogen-Ion Concentration; D020411:Oligonucleotide Array Sequence Analysis; D010641:Phenotype; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D025341:Principal Component Analysis; D017494:Proton Pumps / Q000235:genetics / Q000378:metabolism*; D060888:Real-Time Polymerase Chain Reaction
chemical_list: D010940:Plant Proteins; D017494:Proton Pumps; D019343:Citric Acid