Main candidates for the precursors of the proto-Greeks in the ancient DNA record to date

Thanks to the recent release of the Mathieson et al. 2018 dataset (see here), I've been able to spot a very interesting northwest to southeast genetic cline running from the oldest Peloponnese Neolithic (Peloponnese_N) individuals to the Bronze Age Anatolians (Anatolia_BA). Here it is, highlighted in my Principal Component Analysis (PCA) of ancient West Eurasian variation. The relevant datasheet