CLE25 peptide regulates phloem initiation in Arabidopsis through a CLERK‐CLV2 receptor complex

Abstract

The phloem, located within the vascular system, is critical for delivery of nutrients and signaling molecules throughout the plant body. Although the morphological process and several factors regulating phloem differentiation have been reported, the molecular mechanism underlying its initiation remains largely unknown. Here, we report that the small peptide‐coding gene, CLAVATA 3 (CLV3)/EMBEYO SURROUNDING REGION 25 (CLE25), the expression of which begins in provascular initial cells of 64‐cell‐staged embryos, and continues in sieve element‐procambium stem cells and phloem lineage cells, during post‐embryonic root development, facilitates phloem initiation in Arabidopsis. Knockout of CLE25 led to delayed protophloem formation, and in situ expression of an antagonistic CLE25G6T peptide compromised the fate‐determining periclinal division of the sieve element precursor cell and the continuity of the phloem in roots. In stems of CLE25G6T plants the phloem formation was also compromised, and procambial cells were over‐accumulated. Genetic and biochemical analyses indicated that a complex, consisting of the CLE‐RESISTANT RECEPTOR KINASE (CLERK) leucine‐rich repeat (LRR) receptor kinase and the CLV2 LRR receptor‐like protein, is involved in perceiving the CLE25 peptide. Similar to CLE25, CLERK was also expressed during early embryogenesis. Taken together, our findings suggest that CLE25 regulates phloem initiation in Arabidopsis through a CLERK‐CLV2 receptor complex.

Abscisic acid dynamics, signaling, and functions in plants

“…The recently developed markers and reporters can facilitate these analyses (Duan et al 2013; Jones et al 2014; Waadt et al 2014; Wu et al 2018). Beside the Ca 2+ and ROS signals, the small peptide CLE25 may also participate in the long‐distance delivery of stress signals to promote ABA biosynthesis in leaves (Ren et al 2019).…”

A little goes a long way: CLE peptides mediate phloem initiation

“…This dominant negative transgenic has a short‐root phenotype, delayed phloem initiation and compromised phloem continuity and differentiation, consistent with but more drastic than the null mutant (Figure ). Furthermore, they find that the CLERK receptor kinase functions together with CLV2 to perceive the CLE25 peptide and provide evidence that CLV2 and CLERK form complexes in vivo (Ren et al ).…”

“… Short‐root phenotype of CLE25 G6T In contrast to the wild‐type Arabidopsis seedlings (left), the CLE25 G6T seedling (right) exhibits a short‐root phenotype. Figure 1 from Ren et al (), figure 2A.…”

“…However, the high level of redundancy among CLE peptides as well as the unique nature of phloem cells make it difficult to explore the role of CLE peptides in phloem initiation. New work by Ren et al () uses an antagonistic CLE peptide technology to reveal a role for CLE25 in phloem initiation.…”

“…The organization of the phloem is a tightly regulated process which must be properly initiated in order to have continuity from the shoot to the root. Work by Ren et al () shows the importance of the CLE25 peptide acting via the CLV2/CRN/CLERK complex in mediating this process and suggests that several different CLE peptides can contribute to overall phloem differentiation. It will be of interest to see how the different CLE peptides engage the receptor perception machinery to achieve this function.…”