Abstract
In plants, many signalling molecules, such as phytohormones, miRNAs, transcription factors, and small signalling peptides, drive growth and development. However, very few small signalling peptides have been shown to be necessary for lateral root development. Here, we describe the role of the peptide RALFL34 during early events in lateral root development, and demonstrate its specific importance in orchestrating formative cell divisions in the pericycle. Our results further suggest that this small signalling peptide acts on the transcriptional cascade leading to a new lateral root upstream of GATA23, an important player in lateral root formation. In addition, we describe a role for ETHYLENE RESPONSE FACTORs (ERFs) in regulating RALFL34 expression. Taken together, we put forward RALFL34 as a new, important player in lateral root initiation.
Highlights
Root plasticity is one of the main adaptive traits enabling plants to cope with an ever-changing environment
In a transcriptome analysis focusing on early stages of lateral root initiation and utilizing a lateral root inducible system based on auxin treatment leading to synchronous induction of lateral roots (Himanen et al, 2002, 2004; De Rybel et al, 2010), RALF-LIKE 34 (RALFL34) (AT5G67070) expression was up-regulated, together with a small set of 14 potential key regulatory genes for asymmetric cell division and/or cell fate specification during lateral root initiation, including ARABIDOPSIS CRINKLY4 (ACR4) (De Smet et al, 2008) (Fig. 1A)
A more detailed analysis quantifying the different stages of lateral root development in ralfl34-1 and ralfl34-2 revealed that this is probably due to an enrichment of stage 1 lateral root primordia [which included regions with divisions that did not fully resemble a typical stage 1 primordium] compared with the control (Fig. 2B)
Summary
Root plasticity is one of the main adaptive traits enabling plants to cope with an ever-changing environment. Lateral roots are formed post-embryonically from the pericycle cells adjacent to the xylem poles (Malamy and Benfey, 1997; Dubrovsky et al, 2001; De Smet et al, 2006). Their initiation and development occur in a regular way, and depend largely on the plant hormone auxin (Laskowski et al, 1995; Malamy and Benfey, 1997; Beeckman et al, 2001; Casimiro et al, 2001; Lavenus et al, 2013). Less information is known on cellular communication during lateral root development, through the relatively recently discovered small signalling peptides
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