To cite package ‘Guitar’ in publications use:

  X. Cui, Z. Wei, L. Zhang, H. Liu, L. Sun, S.W. Zhang, Y. Huang, and
  J. Meng, Guitar: an R/Bioconductor package for gene annotation guided
  transcriptomic analysis of RNA related genomic features, BioMed
  Research International, 2016

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Guitar: an R/Bioconductor package for gene annotation guided transcriptomic analysis of RNA related genomic features},
    author = {Xiaodong Cui and Zhen Wei and Lin Zhang and Hui Liu and Lei Sun and shao-Wu Zhang and Yufei Huang and Jia Meng},
    year = {2016},
    journal = {BioMed Research International},
  }