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The bZIP53-IAA4 module inhibits adventitious root development in Populus.

ABSTRACT: Adventitious roots (ARs) are important for some plants that depend on clonal propagation. In this study, we demonstrate that a salt-responsive gene module is involved in the negative regulation of AR development in poplar. In this module, the expression of bZIP53 is induced by salt stress and it encodes a transcription factor with transactivation activity. Overexpression or induced expression of bZIP53 in poplar lines resulted in inhibition of AR growth, while heterologous overexpression of bZIP53 in Arabidopsis resulted in a similar phenotype. Results from RNA-seq and RT-qPCR assays predicted IAA4-1 and IAA4-2 to be downstream genes that were regulated by bZIP53. Further investigation of protein-DNA interactions using yeast one-hybrid, electrophoretic mobility shift, dual luciferase reporter, and GUS co-expression assays also showed that IAA4-1/2 were the genes that were directly regulated by bZIP53. Induced-expression IAA4-1/2 transgenic poplar lines also showed inhibited AR growth. In addition, both poplar bZIP53 and IAA4-1/2 showed a response to salt stress. On the basis of these results, we conclude that the bZIP53-IAA4 module is involved in the negative regulation of AR development in poplar.

SUBMITTER: Zhang Y

PROVIDER: S-EPMC7307859 | biostudies-literature | 2020 Jun

REPOSITORIES: biostudies-literature

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The bZIP53-IAA4 module inhibits adventitious root development in Populus.

Zhang Yan Y Yang Xiaoqing X Cao Pei P Xiao Zheng'ang Z Zhan Chang C Liu Meifeng M Nvsvrot Tashbek T Wang Nian N

Journal of experimental botany 20200601 12

Adventitious roots (ARs) are important for some plants that depend on clonal propagation. In this study, we demonstrate that a salt-responsive gene module is involved in the negative regulation of AR development in poplar. In this module, the expression of bZIP53 is induced by salt stress and it encodes a transcription factor with transactivation activity. Overexpression or induced expression of bZIP53 in poplar lines resulted in inhibition of AR growth, while heterologous overexpression of bZIP ...[more]

PMID: 32076710

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Project description:BackgroundAdventitious roots (AR) develop from tissues other than the primary root, in a process physiologically regulated by phytohormones. Adventitious roots provide structural support and contribute to water and nutrient absorption, and are critical for commercial vegetative propagation of several crops. Here we quantified the number of AR, root architectural traits and root biomass in cuttings from a pseudo-backcross population of Populus deltoides and Populus trichocarpa. Quantitative trait loci (QTL) mapping and whole-transcriptome analysis of individuals with alternative QTL alleles for AR number were used to identify putative regulators of AR development.ResultsParental individuals and progeny showed extensive segregation for AR developmental traits. Quantitative trait loci for number of AR mapped consistently in the same interval of linkage group (LG) II and LG XIV, explaining 7-10 % of the phenotypic variation. A time series transcriptome analysis identified 26,121 genes differentially expressed during AR development, particularly during the first 24 h after cuttings were harvested. Of those, 1929 genes were differentially regulated between individuals carrying alternative alleles for the two QTL for number of AR, in one or more time point. Eighty-one of these genes were physically located within the QTL intervals for number of AR, including putative homologs of the Arabidopsis genes SUPERROOT2 (SUR2) and TRYPTOPHAN SYNTHASE ALPHA CHAIN (TSA1), both of which are involved in the auxin indole-3-acetic acid (IAA) biosynthesis pathway.ConclusionsThis study suggests the involvement of two genes of the tryptophan-dependent auxin biosynthesis pathway, SUR2 and TSA1, in the regulation of a critical trait for the clonal propagation of woody species. A possible model for this regulation is that poplar individuals that have poor AR formation synthesize auxin indole-3-acetic acid (IAA) primarily through the tryptophan (Trp) pathway. Much of the Trp pathway flux appears to be directed to the synthesis of indole glucosinolates (IG), as suggested by the over-expression of SUR2. Individuals that are efficient in AR formation may utilize alternative (non-Trp) pathways to synthesize IAA, based on the observation that they down-regulate the expression of TSA1, one of the critical steps in the synthesis of tryptophan.

Project description:Stem cuttings of P. trichocarpa (clone 101-74) were rooted in liquid medium without growth regulators (basal medium). The first emerging roots were observed on cuttings 6 days after the start of culture. The highest average root number per cutting (10 Â± 2 roots/cutting) was obtained after 14 days. The first macroscopic evidence of root initiation was the appearance of root primordia, as lateral bulges observed at the stem surface 3 to 4 days after transfer to basal medium. Stem cross-sections showed intensely dividing cells forming root primordial. One to two days later the bark split and the organized sequence of cell division and differentiation steps in the primordium led to the establishment of the main root tissues, as well as the vascular connections of the incipient root with the pre-existing stem vasculature. Subsequently, the outgrowth and emergence of the adventitious root occurred. We refer to the dormant cutting as stage 0, the organizing primordium as stage 1, the primordium differentiation as stage 2. To examine changes in gene transcription associated with the development of adventitious roots, we monitored the transcript levels in differentiating primordia using microarrays. cDNA was prepared from replicate sets of P. trichocarpa rooted cuttings harvested at stages 0, 1 and 2. The Populus whole-genome expression array version 2.0 manufactured by NimbleGen Systems Limited (Madison, WI) contains in duplicates three independent, non-identical, 60-mer probes per whole gene model plus control probes and labeling controls. Included in the microarray are 65,965 probe sets corresponding to 55,970 gene models predicted on the P. trichocarpa genome sequence version 1.0 and 9,995 aspen cDNA sequences (Populus tremula, Populus tremuloides, and P. tremula x P. tremuloides). NimbleGen whole genome microarray analyses were performed in triplicate as per manufacturers instructions. We carried out nine hybridizations (NimbleGen) with samples derived from three early developmental stages of P. trichocarpa adventitious roots. cDNA was synthesized using CLONTECH Smart cDNA Synthesis kit containing an amplification step on the cDNA level. All samples were labeled with Cy3.

Project description:Adventitious root formation at the base of plant cuttings is an innate de novo organogenesis process that allows massive vegetative propagation of many economically and ecologically important species. The early molecular events following shoot excision are not well understood. Using whole-genome microarrays, we detected significant transcriptome remodeling during 48 hours following shoot removal in Populus softwood cuttings in the absence of exogenous auxin, with 27% and 36% of the gene models showing differential abundance between 0 and 6 hours, and 6 and 24 hours, respectively. During these two time intervals, gene networks involved in protein turnover, protein phosphorylation, molecular transport and translation were among the most significantly regulated. Transgenic lines expressing a constitutively active form of the Populus type-B response regulator PtRR13 (ÎDDKPtRR13) have a delayed rooting phenotype and cause misregulation of COV1, a negative regulator of vascularization; PDR9, an auxin efflux transporter; two AP2/ERF genes with sequence similarity to TINY1. Cytokinin action appeared to disrupt root development 24 hours after shoot excision, when root founder cells are hypothesized to be sensitive to the negative effects of cytokinin. Our results suggest that PtRR13 acts downstream of cytokinin to repress adventitious root formation in intact plants, and that reduced cytokinin signaling after shoot excision enables coordinated expression of ethylene, auxin and vascularization pathways leading to adventitious root development. Populus tremula x Populus alba INRA-clone No. 717-1-B4 plants expressing a constitutively active form of the Populus type-B response regulator PtRR13 (ÎDDKPtRR13) were generated via an Agrobacterium-mediated protocol developed by Han et al. (2000). Non-transgenic and ÎDDKPtRR13 line were grown to a height of 60 cm. A 14 cm tall apical cuttings were collected from the mother plants. Cuttings were placed in 25 cm2 pots Fafard mix #4 and placed on a mist bench with intermittent mist to prevent shoot desiccation. Samples were collected at the indicated time points and consisted of a 5 mm section measured up from the base of the cutting (one sample per cutting). Total RNA was extracted with the RNeasy mini kit (Qiagen USA) and DNase treated in-column with the RNase-Free DNase set (Qiagen USA). Double-stranded cDNA was synthesized using SuperScript Double Strand cDNA Synthesis Kit (Invitrogen USA, Carlsbad, CA) with oligo-dT primers following the manufacturerâs protocol except that the synthesis step was extended to 16 hours. Cy-3 labeling and hybridization steps were performed by NimbleGen using their standard procedures. A custom-designed microarray platform was used comprising single 60-mer probes designed against 55,793 annotated gene models from the sequenced genome of P. trichocarpa. Each 60-mer probe was chosen form a group of 6-7 non-overlapping probes designed against different parts of the gene model. The probe whose value was the most similar to the average of 6-7 experimental probes was assumed to be the most reliable for transcript level estimation. A total of 39 microarray chips were used in these experiments: 39 chips = 2 genotypes (NT and ÎDDK) x 4 time points (0, 6, 24 and 48 hours) x 5 biological replications, except for the 0 hour ÎDDK where 4 biological replications were used. Signal intensities were log2 transformed and quantile normalized (Sugiharto et al., 1992). Normalized signals were analyzed in SAS 9.1 (SAS Institute, Cary, NC) using a mixed model analysis of variance (ANOVA) with genotype and genotype by time interactions as fixed effects, and biological replication as a random effect.

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The bZIP53-IAA4 module inhibits adventitious root development in Populus.

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The bZIP53-IAA4 module inhibits adventitious root development in Populus.

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