Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:1 3 of R2R3 and R3-MYB transcription factors is capable to suppress flavonoids in model plants such as tobacco and Arabidopsis (Aharoni et al. 2001; Matsui et al. 2008; Zhu et al. 2009, 2013; Albert et al. 2011; Nakatsuka et al. 2013).
Category: