Arabidopsis ZUOTIN RELATED FACTOR1 Proteins Are Required for Proper Embryonic and Post-Embryonic Root Development

Abstract

The H2A/UBIQUITIN-binding proteins AtZRF1a/b have been reported as key regulators involved in multiple processes of Arabidopsis plant growth and development. Yet, the cellular and molecular mechanisms underlying the mutant phenotype remain largely elusive. Here we show that loss-of-function of AtZRF1a/b causes defective root elongation and deformed root apical meristem organization in seedlings. The premature termination of the primary root in the atzrf1a;atzrf1b double mutant is associated with an advanced onset of endoreduplication and subsequent consumption of reservoir stem cells. Cytological analyses using cell type-specific markers and florescent dyes indicate that AtZRF1a/b are involved in maintenance of proper cell layer organization, determinacy of cell identity, and establishment of auxin gradient and maximum at the root tip. During embryogenesis AtZRF1a/b act dominantly in regulating the maintenance of ground tissue initial cells and production of lateral root cap. Lastly, quantitative real-time polymerase chain reaction analysis shows mis-expression of some key genes involved in regulating cell patterning, cell proliferation and/or hormone pathways. Our results provide important insight into AtZRF1a/b function in cell fate determinacy and in establishment and maintenance of proper stem cell reservoir during embryonic and post-embryonic root development.

A Novel Epigenetic Regulator ZRF1: Insight into Its Functions in Plants

“…Moreover, in mutants, the cortex layer showed low or no CO2::H2B-YFP expression. All these results indicated that AtZRF1a/b plays a crucial role in the establishment and maintenance of cell fate of various cell types in RAM [42]. The atzrf1a atzrf1b double mutants showed increased expression of several key root regulatory genes, including WOX5 and ERF115 (associated with dividing quiescent center cells) [43].…”

“…Analysis of ploidy levels and the expression levels of cell cycle genes (e.g., CYCD4;1, KRP6) in atzrf1a atzrf1b double mutants true leaves showed that AtZRF1a/b inhibited the transition of mitosis to the endocycle [22]. Moreover, the mutant roots displayed low mitotic activities and elevated polyploid levels [42]. These results indicated that AtZRF1a/b is involved in the regulation of the cell cycle programme.…”

“…In atzrf1a atzrf1b double mutants, the length of primary roots was only 1/3 that of the wild type, and many adventitious roots were produced [23,42]. The size of RAM in mutants was smaller than that in the wild type.…”

“…In the determination of plant growth sensitivity to auxin treatment, it was found that the atzrf1a atzrf1b double mutants were more sensitive than the wild type, based on the addition of exogenous1-naphthlcetic acid. Furthermore, the auxin response reporter DR5rev::GFP was introgressed into the atzrf1a atzrf1b double mutants, and it was found that the loss of function of ZRF1a/b had a negative effect on auxin distribution [42]. The cytokininresponse reporter TCS::GFP was introgressed into the atglsa1-3 atglsa2-1 double mutants, and the results showed that the localization of cytokinin changed in mutants [23].…”

“…It is well known that plant hormones are important in root development. The atzrf1a atzrf1b double mutants were observed to be involved in abnormal root development [23,42]. In the determination of plant growth sensitivity to auxin treatment, it was found that the atzrf1a atzrf1b double mutants were more sensitive than the wild type, based on the addition of exogenous1-naphthlcetic acid.…”