The seedings were aligned onto a 2% agarose plate for root tips collection. Using an ophthalmic scalpel (Feather), the meristematic zone of the seedlings were precisely dissected under a dissecting microscope (Axio Zoom, Zeiss). Total RNA was extracted from 50 root sections using the RNeasy Micro Kit (Qiagen). All total RNA samples were treated with DNaseI during RNA extraction. RNA libraries were prepared using Universal RNA-Seq with NuQuant library preparation kit following manufacture's protocols