背景回顾：Lateral roots are important for a wide range of processes, including water and nutrients uptake. The CLAVATA3 (CLV3)/EMBRYO SURROUNDING REGION-RELATED (CLE) 1~7 peptide family and their cognate receptor CLV1 have been shown to negatively regulate lateral root formation under low nitrate conditions. 

提出问题：However, little is known about how CLE signaling regulates lateral root formation. A persistent obstacle in CLE peptide research is their functional redundancies, which makes functional analyses difficult.  

主要研究：To address this problem, we generate the cle1~7 septuple mutant (cle1~7-cr1, cr stands for mutant allele generated with CRISPR/Cas9). 

结果1-CLE高阶突变促进侧根形成：cle1~7-cr1 exhibits longer lateral roots under normal condition. Specifically, in cle1~7-cr1, the lateral root density is increased, and lateral root primordia initiation is found to be accelerated. Further analysis shows that cle3 single mutant exhibits slightly longer lateral roots. 

结果2-CLE2/3过表达抑制侧根形成：On the other hand, plants that overexpress CLE2 and CLE3 exhibit decreased lateral root lengths. 

结果3-CLE2/3受体CLV1和BAM1：To explore cognate receptor(s) of CLE2 and CLE3, we analyze lateral root lengths in clv1 bam1 (barely any meristem 1) double mutant. Mutating both the CLV1 and BAM1 causes longer lateral roots, but not in each single mutant. In addition, genetic analysis reveals that CLV1 and BAM1 are epistatic to CLE2 and CLE3.

结果4-CLE-CLV1/BAM1-LBDs：Furthermore, gene expression analysis shows that the LATERAL ORGAN BOUNDARIES DOMAIN/ASYMMETRIC LEAVES2-LIKE (LBD/ASL) genes, which promote lateral root formation, are upregulated in cle1~7-cr1 and clv1 bam1. 

结论：We therefore propose that CLE2 and CLE3 peptides are perceived by CLV1 and BAM1 to mediate lateral root formation through LBDs regulation.

侧根对于植物吸收水分和营养等多个过程十分重要。CLE多肽家族及其受体CLV1被认为在低氮条件下，参与侧根形成的负调控。但是，有关CLE信号转导如何调控侧根的形成所知甚少。研究CLE多肽功能的其中一个障碍就是该家族存在严重的功能冗余，从而导致了分析功能的困难。为了解决这个问题，作者创制了cle1~7七突变体cle1~7-cr1，该突变体在正常条件下存在侧根变长的表型。进一步分析显示，cle1~7-cr1突变体的侧根密度增加，并且侧根原基的起始被加速。作者发现cle3单突植株存在侧根稍微变长的表型。另外，过表达CLE2和CLE3会降低侧根的长度。为了挖掘CLE2和CLE3的受体，作者分析了clv1 bam1双突植株的侧根长度。CLV1和BAM1两个基因的功能缺失突变会导致侧根变长，但是单突不会。另外，遗传分析显示CLV1和BAM1对于CLE2/3来说是上位性的。此外，基因表达分析显示促进侧根形成的基因LBD/ASLs在cle1~7-cr1和clv1 bam1突变体中均上调表达。因此，作者提出植物CLE2和CLE3多肽被CLV1和BAM1感知，然后通过对LBDs基因的表达调控，介导侧根的形成。

** Shinichiro Sawa **