Expression of KNUCKLES in the Stem Cell Domain Is Required for Its Function in the Control of Floral Meristem Activity in Arabidopsis.

Kamila Kwaśniewska,Bennett Thomson,Nathanaël Prunet,Christina Fitzsimons,Diarmuid S Ó’Maoiléidigh,Kevin Goslin,Andrea Finocchio,Frank Wellmer,Caoilfhionn Breathnach,Joseph Beegan

doi:10.3389/fpls.2021.704351

Kamila Kwaśniewska, Bennett Thomson + Show 8 more

Open Access

https://doi.org/10.3389/fpls.2021.704351

Copy DOI

Abstract

In the model plant Arabidopsis thaliana, the zinc-finger transcription factor KNUCKLES (KNU) plays an important role in the termination of floral meristem activity, a process that is crucial for preventing the overgrowth of flowers. The KNU gene is activated in floral meristems by the floral organ identity factor AGAMOUS (AG), and it has been shown that both AG and KNU act in floral meristem control by directly repressing the stem cell regulator WUSCHEL (WUS), which leads to a loss of stem cell activity. When we re-examined the expression pattern of KNU in floral meristems, we found that KNU is expressed throughout the center of floral meristems, which includes, but is considerably broader than the WUS expression domain. We therefore hypothesized that KNU may have additional functions in the control of floral meristem activity. To test this, we employed a gene perturbation approach and knocked down KNU activity at different times and in different domains of the floral meristem. In these experiments we found that early expression in the stem cell domain, which is characterized by the expression of the key meristem regulatory gene CLAVATA3 (CLV3), is crucial for the establishment of KNU expression. The results of additional genetic and molecular analyses suggest that KNU represses floral meristem activity to a large extent by acting on CLV3. Thus, KNU might need to suppress the expression of several meristem regulators to terminate floral meristem activity efficiently.

Highlights

The maintenance of stem cells in the shoot apical meristem is crucial for the growth and development of plants
In the model plant Arabidopsis thaliana, genes involved in the CLAVATA–WUSCHEL pathway play a key role in the maintenance of shoot meristem activity and size by forming a regulatory feedback loop that connects the stem cell
KNU expression has been reported to commence at stage 6 of flower development in the stem cell domain as well as in cells of the underlying organizing center (Payne et al, 2004; Sun et al, 2009, 2019), which is crucial for meristem maintenance

Summary

Introduction

The maintenance of stem cells in the shoot apical meristem is crucial for the growth and development of plants. Termination of Floral Stem Cells by KNU domain in the central zone of the shoot meristem with a group of underlying cells termed the organizing center (Kitagawa and Jackson, 2019). These genes include, among others, CLAVATA1 (CLV1), CLAVATA2 (CLV2), CLAVATA3 (CLV3), and WUSCHEL (WUS). CLV3, which is expressed in the stem cells, encodes a small protein (Fletcher et al, 1999) that is proteolytically processed into a 12-amino acid peptide (Ito et al, 2006). A return signal from the organizing center to the stem cells is provided directly by WUS, a homeodomain transcription factor (Mayer et al, 1998), which has been shown to move through plasmodesmata into the stem cell domain (Yadav et al, 2011; Daum et al, 2014) where it promotes CLV3 expression (Brand et al, 2000; Schoof et al, 2000)

Methods

Results

Conclusion