Off topic:Shell script make FASTA format to single line including ID and sequence

Question

[SheelS]

A FASTA format usually looks like below.

>seq1
ATGC
>seq2
GCTA
>seq3
GTAC
......
....
..

How to make it showing as single line using shell script? The ID and sequence are separated by Tab.

>seq1    ATGC
>seq2    GCTA
>seq3    GTAC
.......
....
..

I found most likely answer but not working for me.

awk 'NR%4{printf $0" ";next;}1' input.fasta

Anyone can help please?