The peptide SCOOP12 acts on reactive oxygen species homeostasis to modulate cell division and elongation in Arabidopsis primary root.

Small secreted peptides have been described as key contributors to complex signalling networks that control plant development and stress responses. The Brassicaceae-specific PROSCOOP family encodes precursors of Serine riCh endOgenOus Peptides (SCOOPs). In Arabidopsis SCOOP12 has been shown to promote the defence response against pathogens and to be involved in root development. Here, we explore its role as a moderator of Arabidopsis primary root development. We show that the PROSCOOP12 null mutation leads to longer primary roots through the development of longer differentiated cells while PROSCOOP12 overexpression induces dramatic plant growth impairments. In comparison, the exogenous application of synthetic SCOOP12 peptide shortens roots through meristem size and cell length reductions. Moreover, superoxide anion (O2·-) and hydrogen peroxide (H2O2) production in root tips vary according to SCOOP12 abundance. By using reactive oxygen species scavengers that suppress the proscoop12 phenotype, we showed that root growth regulation by SCOOP12 is associated with reactive oxygen species metabolism. Furthermore, our results suggest that peroxidases act as potential SCOOP12 downstream targets to regulate H2O2 production, which in turn triggers cell wall modifications in root. Finally, a massive transcriptional reprogramming, including the induction of genes from numerous other pathways, including ethylene, salicylic acid, and glucosinolates biosynthesis, was observed, emphasizing its dual role in defence and development.

An Erwinia amylovora inducible promoter for improvement of apple fire blight resistance.

KEY MESSAGE: pPPO16, the first Ea-inducible promoter cloned from apple, can be a useful component of intragenic strategies to create fire blight resistant apple genotypes. Intragenesis is an important alternative to transgenesis to produce modified plants containing native DNA only. A key point to develop such a strategy is the availability of regulatory sequences controlling the expression of the gene of interest. With the aim of finding apple gene promoters either inducible by the fire blight pathogen Erwinia amylovora (Ea) or moderately constitutive, we focused on polyphenoloxidase genes (PPO). These genes encode oxidative enzymes involved in many physiological processes and have been previously shown to be upregulated during the Ea infection process. We found ten PPO and two PPO-like sequences in the apple genome and characterized the promoters of MdPPO16 (pPPO16) and MdKFDV02 PPO-like (pKFDV02) for their potential as Ea-inducible and low-constitutive regulatory sequences, respectively. Expression levels of reporter genes fused to these promoters and transiently or stably expressed in apple were quantified after various treatments. Unlike pKFDV02 which displayed a variable activity, pPPO16 allowed a fast and strong expression of transgenes in apple following Ea infection in a Type 3 Secretion System dependent manner. Altogether our results does not confirmed pKFDV02 as a constitutive and weak promoter whereas pPPO16, the first Ea-inducible promoter cloned from apple, can be a useful component of intragenic strategies to create fire blight resistant apple genotypes.