Below is a simple function that takes a data.frame that has a column name and seq and writes a fasta file from it

writeFasta<-function(data, filename){
  fastaLines = c()
  for (rowNum in 1:nrow(data)){
    fastaLines = c(fastaLines, as.character(paste(">", data[rowNum,"name"], sep = "")))
    fastaLines = c(fastaLines,as.character(data[rowNum,"seq"]))
  }
  fileConn<-file(filename)
  writeLines(fastaLines, fileConn)
  close(fileConn)
}
require(dplyr)

exampleData = dplyr::data_frame(name = c("seq1", "seq2", "seq3"),
                                seq = c("AAGGTTTTGCCAA", "TTTTGCCAAGGAA", "TTTAAGGTGCCAA"), 
                                other = c("meta1", "meta2", "meta3"))

writeFasta(exampleData, "example.fasta")