Villain seems tight, he was not involved in a lot of pots.

$0.25/$0.5 Pot Limit Omaha Hi/Lo
9 players
Converted at weaktight.com

Stacks:
Hero ($49.25)
UTG+1 ($93.55)
MP1 ($19.95)
MP2 ($52.60)
MP3 ($63.10)
CO ($51.55)
BTN ($48.15)
SB ($42.25)
BB ($48.70)

Pre-flop: ($0.75, 9 players) Hero is UTG Q 6 A 5
Hero calls $0.5, 3 folds, MP3 raises to $1, CO calls $1, 2 folds, BB calls $0.5, Hero calls $0.5

Flop: 4 Q 7 ($4.25, 4 players)
BB checks, Hero bets $4.25, MP3 calls $4.25, CO calls $4.25, BB folds

Turn: J ($17, 3 players)
Hero checks, MP3 bets $12, 1 fold, Hero ??

additional question : the player is tight, A2xx is highly probable. Let's imagine that i call 12 and a deuce hits the board on the river (it was not what happened on this hand), is it a good idea to shove on bluff/semi bluff with my hand on such a board ?

Tough to say just what villain is holding without a better read, but it sure seems that the turn helped him. He could have something like A24J and made 2 pair to go with his NLD, in which case you are in pretty bad shape. But maybe he just has A2 . It's $12 to call into a $29 pot so it's hard to fold unless you think villain would only bet A24J type hands. If he is the type that would bet just because you checked, then you have to call.

Of course you could have bet the turn yourself, making in hard for a naked A2 to stay in the hand.

You can fold this preflop UTG and be immune to criticism IMO. It's too bad preflop action unfolded the way it did, if he raised anything more you could still have exited there. Flop is too good to fold, and you like the heavy action... fine... but you got a bit nervous, right? Turn is pretty ugly IMO, and I would not continue against a tight player... would against an avg player. If you consider calling the $12 here, why not bet out in range of $12 to pot to dictate and find out if he is in a similar spot as you? Not saying you should have, just suggesting to mull that over. You can continue here, but I hate when I make 2 pair and a bad low on the river when I haven't dictated the action on any street, so I usually preempt those situations in spots like this.

UTG and especially in a full ring game you are prob better off avoiding playing ANY a-5 hands that dont involve aces, no matter how pretty they may look, however u did, so ok....
i think the way you played the hand your are probably better off folding the turn. you are almost never ahead of his range, and a big bet is most likly going to be fired on the river which u will have to fold to unless you greatly improve...If u do call i'd be very hesitant at bluffing if a two came off... this is because u said this is a tight player.. and no tight player i know is potting this turn with a naked a-2...he'd either have two pair with it.. something like a-2-3, prob with clubs or hearts or something along those lines, either way the two on the river will most likly not hurt his hand that baddly, so be very carfully before firing at this river.

the way i would play this hand.. and not saying this is the optimal way, but it seems to work fairly well for me on most occasioons... if i saw this flop, which again i probably wouldnt most times, i'd bet pot on the flop like u did... now the turn is a relative blank, especailly given the most likly hand range of your oponent, so your situation really didnt change much, id now bet three quater pot, something like $8... if i am raised instant muck!!! occasionally this bet will get a weak a-2 to fold, will most likly also fold any pure non nut low draws or weak both way hands, which may have u beat as well... if called my plan would be to fire on any big/repeater card, since a call in this spot tells me my oponent is on some kind of low draw, id even bet if a club hits since its less likly he is on that draw...i'd also obviouly fire to any hand that improves us to the nuts...and id check fold any low card on the river that doesnt improve our standings....

I'd call turn and bet on most rivers about $15. I guess this means I have to call a raise, I wouldn't like it though but I think he calls and chops a lot, or folds a missed low draw sometimes.