Abstract
Plant growth, development, reproduction and environmental stress responses are tightly regulated by a complex network of signalling pathways. Plant hormones - including salicylic acid, ethylene, jasmonic acid, auxins, gibberellins, cytokinins, abscisic acid and brassinosteroids - have long been considered the major signalling molecules during those processes. However, the discovery that many different ( secreted) peptides are involved in signalling has stimulated intensive research, and this special issue reflects the latest developments in this dynamic field.
Highlights
Plant growth, development, reproduction and environmental stress responses are tightly regulated by a complex network of signalling pathways
Small signalling peptides are mainly classified into two groups, the cysteine-rich peptides (CRPs) and post-translationally modified (PTM) peptides
Compared to the exponential growth in knowledge on small signalling peptides, research on the mode of action of plant antimicrobial peptides (AMPs) is limited to a few families, including the defensins, which are characterized by an α-helix and a triple-stranded β-sheet stabilized by four disulfide bridges (Vriens et al, 2014; see a brief description in Bircheneder and Dresselhaus, 2016), and cyclotides, which are cyclic peptides with a head-to-tail backbone and three disulfide bridges
Summary
The CLE peptides are probably the best-studied family of PTM peptides. Mature CLE peptides contain 12 to 13 amino acids and have been found in various plant species. Experiments focusing on transcriptional regulation – something that has been investigated only in a very limited way for small signalling peptides – revealed the involvement of APETALA2/ETHYLENE RESPONSIVE FACTOR (AP2/ERF) transcription factors, downstream of auxin It appears that RALFL34 expression is an earlier marker for lateral root initiation than GATA23, and could play a key role in interpreting a shootderived signal that is involved in positioning lateral roots along the primary root axis. A more recently identified family of PTM peptides are the RGF/CLEL/GLV peptides, with previously assigned roles in root gravitropism, maintenance of the root apical meristem, and root hair, lateral root and shoot development (Matsuzaki et al, 2010; Whitford et al, 2012; Meng et al, 2012; Fernandez et al, 2013, 2015) These peptides are known to promote cell elongation in the growing hypocotyl (Ghorbani et al, 2016). These would greatly benefit from current genome-editing technologies such as the CRISPR/Cas system, allowing specific mutations in the critical coding regions of the peptides (Yamaguchi et al, 2016)
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