How to transfer GRanges object into fasta

I've got a GRanges object , but I don't know how to transfer it into fasta with tx_name.
I tried to extract sequence using writeXStringSet(), but the result didn't have the tx_name. Can anybody tell me how to solve this?

seq <- getSeq(Hsapiens,gr)
writeXStringSet(seq,file="result")

but the result didn't have the tx_name, like follows
>
ATCGATCG

I want to have the tx_name as follows

ENST00000252835.5
ATCGATCG