Total RNA was extracted from the leaves using TRIzol reagents (Life Technologies, CA, USA) supplemented with 0.2 M KOAc, followed by purification with RNeasy Mini Kit (Qiagen, Hilden, Germany). mRNA was enriched from total RNA using Poly(A) Purist MAG Kit (Life Technologies). cDNA libraries were then prepared from the mRNA using SOLiD Total RNA-Seq Kit (Life Technologies), and sequencing was performed by a 5500xl SOLiD according to the standard protocol for 75-base fragment sequencing.