Cell Cycle Progression in the Pericycle Is Not Sufficient for SOLITARY ROOT/IAA14-Mediated Lateral Root Initiation inArabidopsis thaliana 

Abstract

To study the mechanisms behind auxin-induced cell division, lateral root initiation was used as a model system. By means of microarray analysis, genome-wide transcriptional changes were monitored during the early steps of lateral root initiation. Inclusion of the dominant auxin signaling mutant solitary root1 (slr1) identified genes involved in lateral root initiation that act downstream of the auxin/indole-3-acetic acid (AUX/IAA) signaling pathway. Interestingly, key components of the cell cycle machinery were strongly defective in slr1, suggesting a direct link between AUX/IAA signaling and core cell cycle regulation. However, induction of the cell cycle in the mutant background by overexpression of the D-type cyclin (CYCD3;1) was able to trigger complete rounds of cell division in the pericycle that did not result in lateral root formation. Therefore, lateral root initiation can only take place when cell cycle activation is accompanied by cell fate respecification of pericycle cells. The microarray data also yielded evidence for the existence of both negative and positive feedback mechanisms that regulate auxin homeostasis and signal transduction in the pericycle, thereby fine-tuning the process of lateral root initiation.

Integration of responses within and across Arabidopsis natural accessions uncovers loci controlling root systems architecture

“…We found that 104 (P < 0.001) genes or 492 (P < 0.01) genes are more than 1.5-fold differentially expressed compared with the sibling wild type (Table S3). We compared the list of misregulated genes in the rsa1-1 mutant to a list of 3,186 genes regulated by the synthetic auxin naphthalene-1-acetic acid in the root (26). We found significant overrepresentations of the intersections of auxin-regulated genes with genes misregulated in the rsa1-1 mutant for both of our datasets (P < 0.001), compared with random generated gene lists of the same size (27,28), further suggesting a rsa1-1 role in auxin homeostasis.…”

Strigolactones fine-tune the root system

“…This is evidenced in auxin receptor mutants (tir1afb2afb3) that show a drastic reduction in lateral root formation (Dharmasiri et al 2005;Pérez-Torres et al 2008) and in several mutants perturbed in AUX/IAAand ARF-mediated signaling that display severe defects in lateral root organogenesis, or block it completely [in the case of stabilized SOLITARY ROOT(SLR)/IAA14 or loss of ARF7 and ARF19 (Vanneste et al 2005)]. Local accumulation of auxin in root pericycle cells is ensured by PINdependent auxin recirculation inside the root tip (Casimiro et al 2001), a process that is very well described elsewhere and falls beyond the scope of this review.…”

Root system architecture: insights fromArabidopsisand cereal crops

“…Inducing pericycle cells to re-enter the cell cycle through overexpression of D-type cyclins or the G1-S transition-promoting transcription factor E2Fa/ DPa is not sufficient to induce lateral root organogenesis in the absence of further cues determining cell patterning [53]. This control is achieved by fine-tuning the auxin response pathway through AUX/IAA-ARF pairs.…”