The PLO has official status at the UN as the "legitimate representative" of the Palestinian people. In the Seventies it was granted observer status at the UN and it represents the Palestinians in international forums and negotiations with the Israelis.
Before the Nineties there was a logic to this. The PLO was a body composed of a group of different Palestinian organizations and had Arab League support. The Palestinian's were either dispersed or under Israeli rule and had no means of electing a representative and the UN gave that status to the PLO.
Today, however, things have changed. First of all the Palestinians held free elections in 2004. The result of those elections was an indisputable victory not of the PLO, but of Hamas and as such Hamas has the best claim to being the legitimate representative of the Palestinian people. Secondly, Israel has withdrawn from Gaza and Gaza is governed by Hamas. That means that decision making in Gaza is purely by the Palestinians without any outside intervention. While we may not approve of the means by which the Hamas took over in Gaza, and the failure to hold further elections, that is arguably an internal Palestinian affair and despite the problematics Hamas is the only Palestinian group which can claim to represent the Palestinians. At the very least, it is no longer possible to claim that the PLO is the sole representative of the Palestinians or that its decisions are binding on the Palestinians.
It could be argued that in the eyes of the UN the PLO remains the sole representative but in the absence of a fresh decision confirming their status, I would say that is contentious.
At present Israel and the PLO are negotiating a "final solution" to the Israeli-Palestinian conflict under US guidance, but without Hamas having some role in those negotiations, it seems to me that these negotiations cannot be said to be taking place in good faith.
A lot of people feel that Netanyahu is not negotiating in good faith and doesn't really want a result. That may well be the case, but the truth is that the negotiations in their present format are farcical when they don't include the only truly self-governing and independent section of the Palestinian people. As long as that is the case, nobody is acting in good faith.