PROTON1 promoter sequencing
The promoter region of At1g19880 was amplified by PCR with At1g19880_Prom-Fw and At1g19880_Prom-Rv primers (Table S9) for 90 accessions that were part of the initial screen but not the 1001 Genomes dataset (Table S5). For each accession, the fragment of approximately 1500 bp was purified from 0.9 % agarose gel using NucleoSpin Gel and PCR Clean-up columns (Macherey-Nagel GmbH & Co KG, catalog 740609), and Sanger-sequenced using the same primers (LGC, Biosearch Technologies). Sequencing files were evaluated using Chromas v.2.6.6 (Technelysium Pty Ltd).