use Data::Dumper;

my $data = do {local $/;<DATA>};
my $xml  = XMLin($data);

print Dumper $xml;

##</code><code>##

use strict;
use warnings;
use XML::Simple;

my $data = do {local $/;<DATA>};
my $xml  = XMLin($data);

# ... and you use the correct syntax ;)
print $xml->{gene}->{id}, "\n";
print $xml->{gene}->{label}, "\n";

__DATA__
<?xml version="1.0" ?>
<genes>
<gene id = "3" label = "gene_of_interest" />
</genes>