Quality of the unigenes assembled. a, Length ratio of the gap to unigenes assembled by SOAPdenovo and Trinity method, respectively. The x-axis indicates the number of unigenes containing gaps; the y-axis indicates the percentage of the gap length to unigenes length. b, A histogram of the average read-depth coverage for unigenes. The x-axis indicates the number of unigenes, and the y-axis indicates folds distribution of read-depth coverage.