Something like:

#!perl -w
use strict;
my %hash;
for my $line(<DATA>) {
    chomp($line);
    my($key,$val) = split /\t/, $line;
    next unless defined $key and defined $val;
    $hash{$key} .= " $val";
}
print $hash{$_} . "\n" for keys %hash;
__DATA__
A    A_
B    B_
C    C_
D    D_
E    E_
A    A*
B    B*
C    C*
D    D*
E    E*
A    A-
B    B-
C    C-
D    D-
E    E-
A    AB
B    BB
C    CC
D    DD
[download]