  In this note, we define a new invariant of a Legendrian knot in a contact
manifold using an open book decomposition supporting the contact structure. We
define the support genus sg(L) of a Legendrian knot L in a contact 3-manifold
(M, \xi) as the minimal genus of a page of an open book of M supporting the
contact structure \xi such that L sits on a page and the framing given by the
contact structure and by the page agree. We show any null-homologous loose knot
in an overtwisted contact structure has support genus zero. To prove this, we
observe any topological knot or link in any 3-manifold M sits on a page of a
planar open book decomposition of M.
