It's of growing significance in Wales (4)
I believe the answer is:
leek
'significance in wales' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'it's of growing' is the wordplay.
I cannot really see how this works, but
'it' could be 'e' ('e' can mean 'electronic' which is similar to 'IT') and 'e' is found within the answer.
The remaining letters 'lek' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for leek that I've seen before include "Vegetable related to the onion" , "English town" , "Plant (onion relative) eaten as a vegetable" , "Vegetable symbol of Wales" , "Plant related to the onion, pair with potato for soup" .)