Library preparation was adapted from Schanz et al (PMID 25364977). Briefly, cDNA synthesis and the first round of PCR was performed as described. The second PCR was adjusted to the following: 98°C for 2 min; 5 cycles of 95°C 30 sec, 58°C 30 sec, 72°C 50 sec; 3 cycles of 95°C 30 sec, 68°C 30 sec, 72°C 50 sec; 72°C 10 min. Amplicons were visualized on agarose gel, purified by using the QIAquick Gel Extraction Kit (Qiagen), and sequenced on a MiSeq (Illumina)