library_construction_protocol: Frozen root segments from different individuals were ground in liquid nitrogen using sterile mortar and pestles. Total RNA was extracted from samples following the protocol described by Chang et al. (1993). Genomic DNA was removed using the Turbo DNA-free TM reagent (Ambion, Austin, TX, USA), according to the manufacturer's instructions. cDNA libraries were constructed using 2 µg of total RNA and following the TruSeq RNA Sample preparation v.2 kit instructions (Low throughput protocol, Illumina, Inc., CA, USA). Briefly, total RNA samples were polyA-enriched, reverse-transcribed and double-stranded cDNA synthesized. TruSeq adapters were attached to double-stranded cDNA. Enrichment in fragments containing TruSeq adapters on both ends were performed using PCR. The quantity and quality of the enriched libraries were validated using Nanodrop 1000 and Bioanalyzer 2100 respectively. The libraries were normalized to 10 nM of amplicons in 10 mM Tris-HCl, pH 8.5 containing 0.1% Tween 20.