Multiple Peptide signals- and their interplay in growth and defense

Authors: Ashish Marathe¹ Mukesh Kumar Gupta² Rakesh Kumar Prajapat³, Deepak Pawar^3
1 Ph.D Scholar, Division of Biochemistry, IARI, New Delhi-110012
² Ph.D Scholar, Division of Plant Physiology, IARI, New Delhi- 110012
³.Ph.D Scholar, N.R.C.P.B, IARI, New Delhi-110012



In multicellular animal systems, cell to cell interactions are mediated by a variety of extracellular molecules, including peptides and steroids. Similarly, in plants, mobile phytohormones, such as auxins, cytokinins gibberellins, abscisic acid, ethylene and brassinosteroids, have been recognized as major intercellular signals responsible for cell-cell communication. However, the recent discovery of peptides with diverse functions and of their elaborating signalling pathways in plants demonstrates the importance of peptide ligands in plant development. At least four peptides play a vital role in plant cell-cell communication by means of their specific receptors. The first functional plant peptide to be identified was tomato systemin, an 18 amino acid peptide which acts in the rapid expression of defense responsive genes via cellular communication. Later phytosulfokine (PSK), CLAVATA3 and the pollen S determinant S-locus cysteine-rich protein (SCR also called S-locus protein 11, SP11) and other has been discovered. These findings highlight the significance of receptor-mediated peptide signalling in various physiological events in plants, and predict the existence of further peptide-signal-interacting receptor kinases.


Systemin , a systemic inducer of the plant wound response, induces proteinase inhibitor (PI) encoding gene and its expression also activates MAP kinase in several plant species. The latter is released from the wounded cells to the apoplast and transported out of wounded leaf via phloem. In adjacent intact tissue and elsewhere, systemin binds with its receptor present on plasmamembrane. This receptor is a leucine rich repeat protein (LRR) with kinase activity. The systemin receptor complex now gets autophosphorylated and inturn activate a phospholipaseA₂ (PLA₂) also located on plasmamembrane. Action of PLA₂ results in release of linolenic acid from the plasmamembrane, linolenic acid in now converted into jasmonic acid through octadecanoid pathway. Jasmonic acid thus produced activate expression of genes that encode defensive protein( such as a-amylase inhibitors, lectins, proteinase inhibitors). These proteins are antidigestive which greatly hamper digestion of insects and other herbivores and thus provide deterrents to them.


Phytosulfokine
(PSK),a sulfated peptide, derived by post-translational modification and processing from an 89 amino acid precursor protein with a cleavable signal peptide at its N terminus. This factor was identified as a mixture of two small polypeptides named phytosulfokines (PSK_Α and PSK_B) containing two Tyrosine residues each of which both hydroxyl groups are esterified with phosphate. Phytosulfokines have an important regulatory effect on the de-differentiation of cells. Plant cells can retain the ability of totipotency which means that they can be de-differentiated in such a way that they can re-enter the cell cylcle to form all organs of a new plant. Tyrosylprotein sulfotransferase (TPST) is involved in this PSK biosynthesis pathway.


In higher plants, the formation of above-ground organs is controlled by meristems, and the maintenance of these meristems requires a balance between cell proliferation and differentiation, it control by CLAVATA (CLV) genes. CLV1 occurs in two distinct complexes of 185 kDa and 450 kDa. The 450 kDa multimer contains a Rho-GTPase related protein and the kinase associated protein phosphatase (KAPP) in addition to the CLV1 and CLV2 dimer.


SCR
(SP11) is highly polymorphic peptides (74-77 amino acids) encode by the SCR (SP11) genes play role of pollen determinant of self-incompatibility.


The full spectrum of peptide function in plant have not been explore yet, there for we need to discovere yet more plant peptides to improve our understanding of cell-cell communication and their numerous functions.

References:

1. Hiroo, F. and Tetsuya, H. (2011). Diverse function of plant peptides: Entering a new phase. Plant Cell Physiol., 52(1): 1â€"4.

2. Yoshikatsu, M., Heping, Y. and Youji, S. (2001). Peptide signals and their receptors in higher plants. Trends in Plant Science., 6:573-577.

3. Yvonne, S. and Rudiger, S. (2012). Peptides and receptors controlling root development. Phil. Trans. R. Soc. B., 367.

About Author / Additional Info:
Ph.D Scholar in the Division of Biochemistry