CLE peptide

CLE peptides (CLAVATA3/Embryo Surrounding Region-Related) are a group of peptides found in plants that are involved with cell signaling. Production is controlled by the CLE genes. Upon binding to a CLE peptide receptor in another cell, a chain reaction of events occurs, which can lead to various physiological and developmental processes. This signaling pathway is conserved in diverse land plants.^[1]

Background

Plants and animals alike both use small polypeptides for signaling in cell-to-cell communication. CLAVATA3/Embryo Surrounding Region-Related, also known as a plant peptide hormone, signaling is important for cell to cell signaling but also long distance communication. These two actions are especially important for plant cells because they are stationary and must perform cell expansion. In multicellular organisms cell-to-cell communication has been found to be very crucial for many growth processes that occur inside the organism. The 12 or 13 amino acid polypeptides are the mature forms of the CLE proteins that are derived from the conserved CLE domains.^[2]^[3]^[4] More and more CLE genes are being identified with more research being conducted in this area. CLE genes have not only been found in seed plants but also in lycophytes, bryophytes, and green algae.^[5]^[6]

Genes

Most research that has been conducted on CLE peptide signaling has been conducted with Arabidopsis, since this genome contains 32 members of the CLE gene family. CLV3 which belongs to the CLE family of genes is found within one or more tissues of Arabidopsis. All 32 members of the CLE family share two characteristics that include: encoding of a small protein with a putative secretion signal at their N- termini and contain a conserved CLE motif at or near their C-termini.^[7] The 32 members of the CLE gene family originated from mutations of the original gene.

Structures

CLE peptides are coded by the CLE genes. These peptides vary in structure with each peptide structure performing a different job with in the plant. The minimal length of functioning CLE peptides has been found to be 12 amino acids with several critical residues.^[8] There are two different peptide structures that are found within the plant and they are A-type and B-type. When A-type hormones are secreted the plant slows down the rate of root growth whereas the secretion of B-type peptides effects the vascular growth of the plant.^[9] The secretion of A-type peptides speeds up the vascular development of the plant that is mediated by the B-type peptides. This suggests that these two types of peptides work together to regulate the growth of the plant. The specific peptides are:^[8]

A-type peptides

CLE 1/3/4
CLE 2
CLE 5/6
CLE 7
CLE 8
CLE 9
CLE 10
CLE 11
CLE 12
CLE 13
CLE 14
CLE 16
CLE 17
CLE 18
CLE 19
CLE 20
CLE 21
CLE 22
CLE 25
CLE 26
CLE 27
CLE 40
CLE 45

B-type peptides

CLE 41/44/TDIF
CLE 42
CLE 43
CLE 46

Signaling in the shoot apical meristem

Shoot apical meristems of Crassula ovata (left). Fourteen days later, leaves have developed (right).

Tunica-Corpus model of the apical meristem (growing tip). The epidermal (L1) and subepidermal (L2) layers form the outer layers called the tunica. The inner L3 layer is called the corpus. Cells in the L1 and L2 layers divide in a sideways fashion, which keeps these layers distinct, whereas the L3 layer divides in a more random fashion.

Meristematic cells give rise to various organs of the plant and keep the plant growing. There are two types of meristematic tissues 1) Apical Meristem 2) Lateral Meristem. The Apical Meristem is of two types; the shoot apical meristem (SAM) gives rise to organs like the leaves and flowers, while the root apical meristem (RAM) provides the meristematic cells for the future root growth. SAM and RAM cells divide rapidly and are considered indeterminate, in that they do not possess any defined end status. In that sense, the meristematic cells are frequently compared to the stem cells in animals, which have an analogous behavior and function. Within plants SAM cells play a major role in the overall growth and development, this is due to the fact that all cells making up the major parts of the plant come from the shoot apical meristem (SAM). There are three different important area found within the SAM and they include the central zone, the peripheral zone), and the rib meristem. Each of these areas play an important in the production of new stem cells within the SAM. All SAMs are usually dome shaped and have structures that are layered and are described as the tunica and corpus. CLV3 plays an important role in regulating the production of stem cells within the Central Zone region of the (SAM), this is also true for the cell promoting WUSCHEL (WUS) gene. The combination of these two genes regulates stem cell production by WUS negatively or positively regulating the production of stem cells by controlling the CLV3 gene.;^[10]^[11]

Genes in other plants

CLE genes have been found in numerous monocots, dicots, and even moss. Research has even shown that some plants like rice contain the presence of a multi-CLE domain.^[5]^[7] Various CLE-like genes have also been found in the genomes of plant-parasitic nematodes such as beet, soybean and potato cyst nematodes.^[12]^[5]^[13]

References

^ Betsuyaku S, Sawa S, Yamada M (2011). "The Function of the CLE Peptides in Plant Development and Plant-Microbe Interactions". The Arabidopsis Book. 9: e0149. doi:10.1199/tab.0149. PMC 3268505. PMID 22303273.
^ Kondo T, Sawa S, Kinoshita A, Mizuno S, Kakimoto T, Fukuda H, sakagami Y (2006). "A plant peptide encoded by CLV3 identified by in situ MALDI-TOF MS analysis". Science. 313 (5788): 845–48. Bibcode:2006Sci...313..845K. doi:10.1126/science.1128439. JSTOR 3846935. PMID 16902141. S2CID 31119711.
^ Ito Y, Nakanomyo I, Motose H, Iwamoto K, Sawa S, Dohmae N, Fukuda H (August 2006). "Dodeca-CLE peptides as suppressors of plant stem cell differentiation". Science. 313 (5788): 842–5. Bibcode:2006Sci...313..842I. doi:10.1126/science.1128436. PMID 16902140. S2CID 11502739.
^ Ohyama K, Shinohara H, Ogawa-Ohnishi M, Matsubayashi Y (August 2009). "A glycopeptide regulating stem cell fate in Arabidopsis thaliana". Nat. Chem. Biol. 5 (8): 578–80. doi:10.1038/nchembio.182. PMID 19525968.
^ ^a ^b ^c Oelkers K, Goffard N, Weiller GF, Gresshoff PM, Mathesius U, Frickey T (January 2008). "Bioinformatic analysis of the CLE signaling peptide family". BMC Plant Biol. 8: 1. doi:10.1186/1471-2229-8-1. PMC 2254619. PMID 18171480.
^ Miwa H, Tamaki T, Fukuda H, Sawa S (June 2009). "Evolution of CLE signaling: origins of the CLV1 and SOL2/CRN receptor diversity". Plant Signal Behav. 4 (6): 477–81. doi:10.4161/psb.4.6.8391. PMC 2688290. PMID 19816140.
^ ^a ^b Cock JM, McCormick S (July 2001). "A large family of genes that share homology with CLAVATA3". Plant Physiol. 126 (3): 939–42. doi:10.1104/pp.126.3.939. PMC 1540125. PMID 11457943.
^ ^a ^b Yamaguchi YL, Ishida T, Sawa S (2016). "CLE peptides and their signaling pathways in plant development". J. Exp. Bot. 67 (16): 4813–26. doi:10.1093/jxb/erw208. PMID 27229733.
^ Whitford R, Fernandez A, De Groodt R, Ortega E, Hilson P (November 2008). "Plant CLE peptides from two distinct functional classes synergistically induce division of vascular cells". Proc. Natl. Acad. Sci. U.S.A. 105 (47): 18625–30. Bibcode:2008PNAS..10518625W. doi:10.1073/pnas.0809395105. PMC 2587568. PMID 19011104.
^ Brand U, Fletcher JC, Hobe M, Meyerowitz EM, Simon R (July 2000). "Dependence of stem cell fate in Arabidopsis on a feedback loop regulated by CLV3 activity". Science. 289 (5479): 617–9. Bibcode:2000Sci...289..617B. doi:10.1126/science.289.5479.617. PMID 10915624.
^ Schoof H, Lenhard M, Haecker A, Mayer KF, Jürgens G, Laux T (March 2000). "The stem cell population of Arabidopsis shoot meristems in maintained by a regulatory loop between the CLAVATA and WUSCHEL genes". Cell. 100 (6): 635–44. doi:10.1016/s0092-8674(00)80700-x. PMID 10761929.
^ Wang X, Mitchum MG, Gao B, Li C, Diab H, Baum TJ, Hussey RS, Davis EL (March 2005). "A parasitism gene from a plant-parasitic nematode with function similar to CLAVATA3/ESR (CLE) of Arabidopsis thaliana". Mol. Plant Pathol. 6 (2): 187–91. doi:10.1111/j.1364-3703.2005.00270.x. PMID 20565649.
^ Guo Y, Han L, Hymes M, Denver R, Clark SE (September 2010). "CLAVATA2 forms a distinct CLE-binding receptor complex regulating Arabidopsis stem cell specification". Plant J. 63 (6): 889–900. doi:10.1111/j.1365-313X.2010.04295.x. PMC 2974754. PMID 20626648.