RALFs

Abstract

The Discovery of RALFDuring a search for systemins in tobacco, an unrelated peptide factor was discovered that alkalinizes suspension culture medium even more rapidly than systemins. 13 This factor was named RALF, for Rapid ALkalinization Factor. RALF peptide was first purified from tobacco leaves using the suspension cell alkalinization assay, and an N-terminal peptide sequence was obtained. This sequence allowed the identification of a full length tobacco cDNA indicating that the RALF gene encodes a 115 aa secreted preproprotein that is processed to release a 49 aa active peptide from the C-terminus. Highly conserved active RALF peptides were also isolated from tomato and alfalfa cells, and a synthetic peptide based on the tomato sequence was produced. Both native and oxidized synthetic peptides were able to produce alkalinization responses at nanomolar concentrations, but alkylation of the reduced form of the peptide (which prevents formation of disulfide bridges) inactivated the synthetic peptide. A role for RALFs in defense was considered, since both systemins and RALFs induce alkalinization of medium and MAP kinase activation. However, application of RALF peptide to tobacco leaves did not induce a defense response as detectable by the induction of tobacco trypsin inhibitor. Studies using poplar-derived RALFs

Developmental dynamics of Kranz cell transcriptional specificity in maize leaf reveals early onset of C4-related processes

“…Also consistent with this SST-localized and BS-specific developmental pattern are transcripts for the maize homologue of the secondary wall master regulator NST1 (GRMZM2G171395), three lignin biosynthetic genes and a laccase, suggesting that a burst of BS-specific wall strengthening occurs immediately before blade emergence ( Mitsuda et al , 2007 ; Berthet et al , 2011 ; Wang and Dixon, 2012 ). Also sharing this SST-localized, BS-specific pattern are three RALFs (rapid alkalinization factors) generally associated with growth inhibition ( Bedinger et al , 2010 ), and here perhaps terminating cell expansion for BS cells before the source transition.…”

The Genome-Wide Analysis of RALF-Like Genes in Strawberry (Wild and Cultivated) and Five Other Plant Species (Rosaceae)

“…Pearce et al [2] showed that mature peptides were almost 50 aa and contain four highly conserved cysteines in the C-terminus, which are essential for activation and are likely involved in disulfide bridges. The mature peptides also contain other conserved regions, such as the YISY motif near the N-terminus, a GASYY motif between the first and second conserved cysteines, and a PYXRGCS motif that contain the third conserved cysteine residue [3]. The YIXY motif is the key regulatory functional element required for targeting RALF to its putative receptor.…”

Evolution of the RALF Gene Family in Plants: Gene Duplication and Selection Patterns

“… 16 In addition, RALF is a recently discovered family of plant peptide that plays a role in plant cell growth as will be described below. 17 …”