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RALF peptides modulate immune response in the moss Physcomitrium patens

Plants utilize small secreted peptides as important mediators of many processes, from growth and development to response to stress conditions. One of such regulators is the conservative 5 kDa cysteine-rich RALF (Rapid Alkalinization Factor) peptide family, which is widely present in terrestrial plants. RAPID ALKALINIZATION FACTOR (RALFs) are peptides that regulate multiple physiological processes in plants. This peptide family has considerably expanded during land plant evolution, but the role of ancient RALFs in modulating stress responses is unknown

Mamaeva ALyapina IKnyazev A, Golub N, Mollaev T, Chudinova E, Elansky S, Babenko VV, Veselovsky VA, Klimina KM, Gribova T, Kharlampieva D, Lazarev V & Fesenko I

A group of scientists from the Laboratory for Systemic Analysis of Proteins and Peptides of IBCh RAS, together with colleagues from Moscow State University, Peoples' Friendship University of Russia, Center of Physical-Chemical Medicine, and Moscow Institute of Physics and Technology used the moss Physcomitrium patens as a model to gain insight into the role of RALF peptides in the coordination of plant growth and stress response in non-vascular plants. The quantitative proteomic analysis revealed concerted downregulation of M6 metalloprotease and some membrane proteins, including those involved in stress response, in PpRALF1, 2 and 3 knockout (KO) lines. The subsequent analysis revealed the role of PpRALF3 in growth regulation under abiotic and biotic stress conditions, implying the importance of RALFs in responding to various adverse conditions in bryophytes. We found that knockout of the PpRALF2 and PpRALF3 genes resulted in increased resistance to bacterial and fungal phytopathogens, Pectobacterium carotovorum and Fusarium solani, suggesting the role of these peptides in negative regulation of the immune response in P. patens. Comparing the transcriptomes of PpRALF3 KO and wild-type plants infected by F. solani showed that the regulation of genes in the phenylpropanoid pathway and those involved in cell wall modification and biogenesis was different in these two genotypes. Thus, our study sheds light on the function of the previously uncharacterized PpRALF3 peptide and gives a clue to the ancestral functions of RALF peptides in plant stress response. The work was published in Frontiers in Plant Science (IF=6.6).

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