背景回顾：The phloem consists of sieve elements (SEs) and companion cells (CCs). 

主要发现：Here we show that Dof-class transcription factors preferentially expressed in the phloem (phloem-Dofs) are not only necessary and sufficient for SE and CC differentiation, but also induce negative regulators of phloem development, CLAVATA3/EMBRYO SURROUNDING REGION-RELATED25 (CLE25), CLE26 and CLE45 secretory peptides. 

结果：CLEs were perceived by BARELY ANY MERISTEM (BAM)-class receptors and CLAVATA3 INSENSITIVE RECEPTOR KINASE (CIK) co-receptors, and post-transcriptionally decreased phloem-Dof proteins and repressed SE and CC formation. Multiple mutations in CLE-, BAM- or CIK-class genes caused ectopic formation of SEs and CCs, producing an SE/CC cluster at each phloem region. 

结论：We propose that while phloem-Dofs induce phloem cell formation, they inhibit excess phloem cell formation by inducing CLEs. Normal-positioned SE and CC precursor cells appear to overcome the effect of CLEs by reinforcing the production of phloem-Dofs through a positive feedback transcriptional regulation.

植物的韧皮部由筛管分子（SEs）和伴胞细胞（CCs）组成。本文中，作者发现在韧皮部特异性表达的Dof转录因子phloem-Dofs不仅对于SE和CC的分化是充分且必需的，而且能够诱导韧皮部发育负调节因子CLE25/26/45。BAM受体和CIK共受体感知CLEs，通过转录后调控方式降低phloem-Dof含量，抑制SE和CC的形成。CLE、BAM和CIK的多重突变会导致SE和CC的异位形成，在每一个韧皮部区域都会产生一组SE/CC。作者认为，phloem-Dofs在诱导韧皮部细胞形成的同时，能够通过诱导CLEs来抑制过多的韧皮部细胞形成。此外，phloem-Dofs会通过一个正反馈转录调控途径，增强phloem-Dofs的生成，从而克服CLEs的负面影响，从而在恰当的位置形成SE和CC前体细胞。