The Progression of Xylem Vessel Cell Differentiation is Dependent on the Activity Level of VND7 in Arabidopsis thaliana.

Risaku Hirai,Misato Ohtani,Taku Demura,Junko Hasegawa,Sachihiro Matsunaga,Takumi Higaki,Yuto Takenaka,Yuki Sakamoto

doi:10.3390/plants9010039

Abstract

Xylem vessels are important for water conduction in vascular plants. The VASCULAR-RELATED NAC-DOMAIN (VND) family proteins, master regulators of xylem vessel cell differentiation in Arabidopsis thaliana, can upregulate a set of genes required for xylem vessel cell differentiation, including those involved in secondary cell wall (SCW) formation and programmed cell death (PCD); however, it is not fully understood how VND activity levels influence these processes. Here, we examined the Arabidopsis VND7-VP16-GR line, in which VND7 activity is post-translationally activated by treatments with different concentrations of dexamethasone (DEX), a synthetic glucocorticoid. Our observations showed that 1 nM DEX induced weak SCW deposition, but not PCD, whereas 10 or 100 nM DEX induced both SCW deposition and PCD. The decreased chlorophyll contents and SCW deposition were apparent after 24 h of 100 nM DEX treatment, but became evident only after 48 h of 10 nM DEX treatment. Moreover, the lower DEX concentrations delayed the upregulation of VND7 downstream genes, and decreased their induction levels. They collectively suggest that the regulation of VND activity is important not only to initiate xylem vessel cell differentiation, but also regulate the quality of the xylem vessels through VND-activity-dependent upregulation of the PCD- and SCW-related genes.

Highlights

Water conduction is crucial for terrestrial plant species living on dry land
Light modulates VND1–3 activity to regulate the venation of cotyledons during seedling development [7]. These findings collectively suggest that xylem vessel cell differentiation is controlled by multiple layers of VASCULAR-RELATED NAC-DOMAIN (VND)-related regulation, optimizing xylem vessel function in response to the environmental conditions [15]
A decreased chlorophyll content was evident after 72 h of the 10 DEX treatment or 24 h of the 100 nM DEX treatment (Figure 1L,M), both of these treatments resulted in similar chlorophyll contents after 72 h. These results suggest that the lower the DEX concentration, the slower the progression of programmed cell death (PCD)

Summary

Introduction

One of the remarkable achievements of molecular biological research into xylem vessel formation in Arabidopsis thaliana was the identification of the master transcriptional regulators of their differentiation, the VASCULAR-RELATED NAC-DOMAIN (VND) family proteins [9]. A detailed analysis of the pathway functioning downstream of the VND family proteins demonstrated that they directly and/or indirectly upregulate the entire sets of genes required for SCW deposition and PCD [6,14,15,16,17]. The upregulation of the SCW-related genes by the VND proteins is partially mediated by the secondary master regulators MYB46 and MYB83 [18,19,20,21], and multiple MYB transcription factors function downstream in the SCW biosynthesis pathway [14,22,23,24]. Functional analyses of the VND and MYB gene homologs suggested that the VND-MYB-based transcriptional network is well conserved among land plants [14,15], including moss (Physcomitrella patens) [25], pine (Pinus taeda) [26], poplar (Populus trichocarpa) [27,28], and rice (Oryza sativa) [29]

Methods

Discussion

Conclusion