Gibberellin Signaling in the Endodermis Controls Arabidopsis Root Meristem Size

Abstract

Plant growth is driven by cell proliferation and elongation. The hormone gibberellin (GA) regulates Arabidopsis root growth by controlling cell elongation, but it is currently unknown whether GA also controls root cell proliferation. Here we show that GA biosynthetic mutants are unable to increase their cell production rate and meristem size after germination. GA signals the degradation of the DELLA growth repressor proteins GAI and RGA, promoting root cell production. Targeting the expression of gai (a non-GA-degradable mutant form of GAI) in the root meristem disrupts cell proliferation. Moreover, expressing gai in dividing endodermal cells was sufficient to block root meristem enlargement. We report a novel function for GA regulating cell proliferation where this signal acts by removing DELLA in a subset of, rather than all, meristem cells. We suggest that the GA-regulated rate of expansion of dividing endodermal cells dictates the equivalent rate in other root tissues. Cells must double in size prior to dividing but cannot do so independently, because they are physically restrained by adjacent tissues with which they share cell walls. Our study highlights the importance of probing regulatory mechanisms linking molecular- and cellular-scale processes with tissue and organ growth responses.

Longitudinal zonation pattern inArabidopsisroot tip defined by a multiple structural change algorithm

“…This observation is in accordance with many studies where similar criteria to determine the RAM/EZ boundary have been used, and which report meristem length increase beyond 5 d after germination (DAG) and later (Galinha et al, 2007;Ubeda-Tomas et al, 2009;Gonzalez-Garcıa et al, 2011;Makkena and Lamb, 2013). Moreover, a kinematic analysis of the arabidopsis root showed that accelerated root growth is mainly due to an increased cell production rate during the first 14 DAG and a steady increase in meristem length during the first 2 weeks of growth after germination (Beemster and Baskin, 1998).…”

The plant‐specific CDKB 1‐ CYCB 1 complex mediates homologous recombination repair in Arabidopsis

“…Primer sequences are indicated in Table EV1. The CYCB1;1 construct was described in Ubeda‐Tomás et al (2009). …”

DELLA Signaling Mediates Stress-Induced Cell Differentiation in Arabidopsis Leaves through Modulation of Anaphase-Promoting Complex/Cyclosome Activity

“…In roots, the average cell cycle duration is constant, and changes in cell production rates are mostly due to changes in the number of dividing cells and thus in the meristem size (Baskin, 2000). Correspondingly, DELLAs induce cell differentiation in the root, thereby making the root meristem smaller and thus decreasing cell production rates (Achard et al, 2009;Ubeda-Tomás et al, 2009;Moubayidin et al, 2010). Recently, the average cell cycle duration in leaves was reported to be constant throughout leaf development as well; therefore, the observed decrease in cell production rates during development is the consequence of a decrease in the fraction of proliferating epidermal cells due to the transition to cell expansion (Asl et al, 2011).…”

“…The 35S::gai-GR construct was made based on a SCR::gai-GR-YFP construct (Ubeda-Tomás et al, 2009), kindly donated by Malcolm Bennett (University of Nottingham), by amplifying gai-GR and cloning this into the Gatewaycompatible pK7WG2 vector (Karimi et al, 2002), and transformed into Columbia-0 plants using Agrobacterium tumefaciens strain C58C1 pMP90. RGA::GFP-RGA, rga-28, and rga-28 gai-2 seeds were kindly provided by Prof. Dr. Tai-ping Sun (Duke University).…”