Default subject in customer reply

[worker]

Hi,

I'm working at otrs 2.4.7,
In customer reply the defual Subject: filed is blank.
How can I modify the system to let the Subject: is filled by Re: original subject.
I have tried the otrs 3.0.0 beta, the subject filed is exactly what I want, but how can I make 2.4.7 to work like 3.0.0.