Untitled

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /plaplo/
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /plaplo/index.php [L]
</IfModule>

I want 
/plaplo/portfolio?catslug=foobar
to look like
/plaplo/portfolio/category/foobar