A deep-coverage BAC library for Ponkan mandarin and its further use in screening ethylene regulated genes

A deep-coverage bacterial artificial chromosome (BAC) library of Yanxiwanlu Ponkan, a late maturing cultivar, was constructed and evaluated. Results showed that the library contained a total of 61,000 clones. Restriction analysis indicated that the DNA insert sizes ranged from 30 to 170 kb with an average of ∼82 kb. No empty clone was found. Therefore, the library should cover ∼13.6-fold of the citrus genome. Continuous sub-cultivation of 5 randomly chosen clones for up to 100 generations showed no detectable change in their restriction profiles. To demonstrate the application of the library in discovery of genes, 7 ethylene-regulated genes were screened by PCR amplification from hierarchically pooled library clones with gene-specific primers. Five positive clones, each representing a different gene, were thus identified from 3840 clones. Sequencing of the clones showed that all of them matched the expected genes, indicating that the library was highly representative.

Research highlights▶ A deep-coverage bacterial artificial chromosome library of Yanxiwanlu Ponkan, an important commercial mandarin cultivar in China, was constructed and evaluated. Results showed that the library contained a total of 61,000 clones. Restriction analysis indicated that the sizes of the exogenous DNA average of ∼82 kb. No empty clone was found. Therefore, the library should cover ∼13.6-fold of the citrus genome. Continuous sub-cultivation of 5 randomly chosen clones for up to 100 generations showed no detectable change in their restriction profiles. To demonstrate the application of the library in discovery of genes, 7 ethylene-regulated genes were screened by PCR amplification from hierarchically pooled library clones with gene-specific primers. Five positive clones, each representing a different gene, were thus identified from 3840 clones. Sequencing of the clones showed that all of them matched the expected genes, indicating that the library was highly representative.