True regarding excitation contraction coupling in smooth muscles is
Troponin is needed for skeletal muscle contraction, not smooth muscle. Sustained contraction occurs due to ‘latch’. 
Myosin needs to be phosphorylated rather than actin for smooth muscle contraction.
Presence of troponin is essential
Sustained contraction occurs with high calcium concentration
Phosphorylation of actin is required for contraction
Presence of cellular calcium is essential to cause muscle contraction