Cytokinin-induced promotion of root meristem size in the fernAzollasupports a shoot-like origin of euphyllophyte roots

The phytohormone abscisic acid (ABA) promotes plant tolerance to major stresses like drought, partly by modulating plant growth and development. However, the underlying mechanisms are poorly understood. Here, we show that cell proliferation in the Arabidopsis thaliana root meristem is controlled by the interplay between three kinases, SNF1-RELATED KINASE 2 (SnRK2), the main driver of ABA signaling, the SnRK1 energy sensor, and the growth-promoting TARGET OF RAPAMYCIN (TOR) kinase. Under favorable conditions, the SnRK1α1 catalytic subunit is enriched in the nuclei of root meristematic cells and this is accompanied by normal cell proliferation and meristem size. Depletion of SnRK2s in a snrk2.2 snrk2.3 double mutant causes constitutive cytoplasmic localization of SnRK1α1 and a reduction in meristem size, suggesting that, under non-stress conditions, SnRK2s enable growth by retaining SnRK1α1 in the nucleus. In response to elevated ABA levels, SnRK1α1 translocates to the cytoplasm and this is accompanied by inhibition of TOR, decreased cell proliferation and meristem size. Blocking nuclear export with leptomycin B abrogates ABA-driven SnRK1α1 relocalization to the cytoplasm and the inhibition of TOR. Fusion of SnRK1α1 to an SV40 nuclear localization signal leads to defective TOR repression in response to ABA, demonstrating that SnRK1α1 nuclear exit is a premise for this repression. Finally, the SnRK2-dependent changes in SnRK1α1 subcellular localization are specific to the proliferation zone of the meristem, underscoring the relevance of this mechanism for growth regulation.

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Root meristem growth factor 1 controls root meristem size through reactive oxygen species signaling

10.1101/244947 ◽

2018 ◽

Cited By ~ 2

Author(s):

Masashi Yamada ◽

Xinwei Han ◽

Philip. N. Benfey

Keyword(s):

Reactive Oxygen Species ◽

Transcription Factor ◽

Stem Cell ◽

Growth Factor ◽

Root Meristem ◽

Reactive Oxygen ◽

Oxygen Species ◽

Meristem Size ◽

Essential Question ◽

Meristem Development

AbstractStem cell niche and root meristem size are maintained by intercellular interactions and signaling networks of a plant peptide hormone, Root Meristem Growth Factor 1 (RGF1). How RGF1 regulates root meristem development is an essential question to understand stem cell function. Although five receptors of RGF1 have recently been identified, the downstream signaling mechanism remains unknown. Here, we report a series of signaling events following RGF1 action. The RGF1-receptor pathway controls distribution of reactive oxygen species (ROS) along the developmental zones of the Arabidopsis root. We identify a novel transcription factor, RGF1 INDUCIBLE TRANSCRIPTION FACTOR 1 (RITF1), which plays a central role in mediating RGF1 signaling. Manipulating RITF1 expression leads to redistribution of ROS along the root developmental zones. Changes in ROS distribution, in turn, enhance the stability of the PLETHORA2 (PLT2) protein, a master regulator of root stem cells. Taken together, our study clearly depicts a signaling cascade initiated by RGF1 and links the RGF1 peptide to ROS regulatory mechanisms.

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Spatial differences in stoichiometry of EGR phosphatase and Microtubule-Associated Stress Protein 1 control root meristem activity during drought stress.

10.1101/2021.10.06.463370 ◽

2021 ◽

Author(s):

Toshisagba Longkumer ◽

Chih-Yun Chen ◽

Marco Biancucci ◽

Bhaskara Govinal Badiger ◽

Paul E. Verslues

Keyword(s):

Cell Division ◽

Cell Size ◽

Cell Expansion ◽

Growth Regulation ◽

Root Meristem ◽

Stress Protein ◽

Root Cell ◽

Root Cortex ◽

Meristem Cell ◽

Meristem Size

During moderate severity drought and low water potential (Ψw) stress, poorly understood signaling mechanisms restrict both meristem cell division and subsequent cell expansion. We found that the Clade E Growth-Regulating 2 (EGR2) protein phosphatase and Microtubule Associated Stress Protein 1 (MASP1) differed in their stoichiometry of expression across the root meristem and had opposing effects on root meristem activity at low Ψw. Ectopic MASP1 or EGR expression increased or decreased, respectively, root meristem size and root elongation during low Ψw stress. This, along with the ability of phosphomimic MASP1 to overcome EGR suppression of root meristem size and observation that ectopic EGR expression had no effect on unstressed plants, indicated that during low Ψw EGR activation and attenuation of MASP1 phosphorylation in their overlapping zone of expression determines root meristem size and activity. Ectopic EGR expression also decreased root cell size at low Ψw. Conversely, both the egr1-1egr2-1 and egr1-1egr2-1masp1-1 mutants had similarly increased root cell size; but, only egr1-1egr2-1 had increased cell division. These observations demonstrated that EGRs affect meristem activity via MASP1 but affect cell expansion via other mechanisms. Interestingly, EGR2 was highly expressed in the root cortex, a cell type important for growth regulation and environmental response.

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