Abstract
Although mechanisms that activate organogenesis in plants are well established, much less is known about the subsequent fine-tuning of cell proliferation, which is crucial for creating properly structured and sized organs. Here we show, through analysis of temperature-dependent fasciation (TDF) mutants of Arabidopsis, root redifferentiation defective 1 (rrd1), rrd2, and root initiation defective 4 (rid4), that mitochondrial RNA processing is required for limiting cell division during early lateral root (LR) organogenesis. These mutants formed abnormally broadened (i.e. fasciated) LRs under high-temperature conditions due to extra cell division. All TDF proteins localized to mitochondria, where they were found to participate in RNA processing: RRD1 in mRNA deadenylation, and RRD2 and RID4 in mRNA editing. Further analysis suggested that LR fasciation in the TDF mutants is triggered by reactive oxygen species generation caused by defective mitochondrial respiration. Our findings provide novel clues for the physiological significance of mitochondrial activities in plant organogenesis.
Highlights
Plants elaborate their architecture by continuously developing new organs, such as leaves, floral organs, axillary stems, and lateral roots (LRs)
These results showed that the LRs of temperature-dependent fasciation (TDF) mutants contain more basal cells in the initial steps of LR development, namely as early as stage II, than normal LRs and indicated that the increase in the number of cells along the lateral axis of the primordium induces the expansion of its central zone, giving rise to an abnormally broadened and flat-shaped LR
As there was no significant increase in LR density (Figure 1I; Kruskal-Wallis test, p>0.3), LR fasciation in the TDF mutants seems to be the result of the expansion of individual primordia, as opposed to the fusion of multiple primordia because of overcrowding that is observed in some other mutants (Benitez-Alfonso et al, 2013; De Smet et al, 2008)
Summary
Plants elaborate their architecture by continuously developing new organs, such as leaves, floral organs, axillary stems, and lateral roots (LRs). Organogenesis begins with the local activation of cell proliferation in the plant body. Proliferation is restricted to certain areas, which is essential for the formation of properly sized and structured organs. The molecular underpinnings of such regulation remain mostly unknown. LRs serve as building blocks of the root system architecture and are crucial for the uptake and transport of water and minerals.
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