Reason to include major road loop for plant (4-1-3)

'plant' is the definition.
(wait-a-bit is a common name for a type of plant)

'reason to include major road loop' is the wordplay.
'reason' becomes 'wit' (wit can mean reason or logic).
'to include' means one lot of letters goes inside another.
'major road' becomes 'AI' (resembles A1, a major road).
'loop' becomes 'tab' (both can mean a piece of material).
'ai'+'tab'='aitab'
'wit' going around 'aitab' is 'WAIT-A-BIT'.

'for' is the link.