BrEXLB1, a Brassica rapa Expansin-Like B1 Gene is Associated with Root Development, Drought Stress Response, and Seed Germination.

Muthusamy Muthusamy,Soo In Lee,Eun Kyung Yoon,Jin A Kim,Joo Yeol Kim

doi:10.3390/genes11040404

Abstract

Expansins are structural proteins prevalent in cell walls, participate in cell growth and stress responses by interacting with internal and external signals perceived by the genetic networks of plants. Herein, we investigated the Brassica rapa expansin-like B1 (BrEXLB1) interaction with phytohormones (IAA, ABA, Ethephon, CK, GA3, SA, and JA), genes (Bra001852, Bra001958, and Bra003006), biotic (Turnip mosaic Virus (TuMV), Pectobacterium carotovorum, clubroot disease), and abiotic stress (salt, oxidative, osmotic, and drought) conditions by either cDNA microarray or qRT-PCR assays. In addition, we also unraveled the potential role of BrEXLB1 in root growth, drought stress response, and seed germination in transgenic Arabidopsis and B. rapa lines. The qRT-PCR results displayed that BrEXLB1 expression was differentially influenced by hormones, and biotic and abiotic stress conditions; upregulated by IAA, ABA, SA, ethylene, drought, salt, osmotic, and oxidative conditions; and downregulated by clubroot disease, P. carotovorum, and TuMV infections. Among the tissues, prominent expression was observed in roots indicating the possible role in root growth. The root phenotyping followed by confocal imaging of root tips in Arabidopsis lines showed that BrEXLB1 overexpression increases the size of the root elongation zone and induce primary root growth. Conversely, it reduced the seed germination rate. Further analyses with transgenic B. rapa lines overexpressing BrEXLB1 sense (OX) and antisense transcripts (OX-AS) confirmed that BrEXLB1 overexpression is positively associated with drought tolerance and photosynthesis during vegetative growth phases of B. rapa plants. Moreover, the altered expression of BrEXLB1 in transgenic lines differentially influenced the expression of predicted BrEXLB1 interacting genes like Bra001852 and Bra003006. Collectively, this study revealed that BrEXLB1 is associated with root development, drought tolerance, photosynthesis, and seed germination.

Highlights

Expansins (EXPs) are cell wall structural proteins which regulate wall expansion during cell growth [1] and stress responses [2] by weakening the hydrogen bond between cell wall polysaccharides.Emerging studies showed that phytohormones interact with the EXPs to coordinate many physiological and cellular processes of plant growth in response to developmental and environmental stimuli [3,4,5].Phytohormones, including cytokinin, jasmonate, and gibberellin, induce the expression of EXP superfamily [6]
The similar exogenous application of phytohormones such as CK, GA3, and JA did not influence the expression of Brassica rapa expansin-like B1 (BrEXLB1) significantly
The results revealed that drought stress, high salinity, osmotic, and oxidative stress conditions upregulated the BrEXLB1 expression significantly at transcriptional level (Figure 1b,c)

Summary

Introduction

Expansins (EXPs) are cell wall structural proteins which regulate wall expansion during cell growth [1] and stress responses [2] by weakening the hydrogen bond between cell wall polysaccharides. Phytohormones, including cytokinin, jasmonate, and gibberellin, induce the expression of EXP superfamily [6]. Genes 2020, 11, 404 membrane H+ -ATPase activity and/or by reducing cell wall pH [7]. It influences the expression of other cell wall-related genes [8]. EXPs participate in abscisic acid-mediated cell growth during drought stress [7]. Enhanced expansin activity could contribute to drought-resistant/tolerant by maintaining higher cell turgor and greater cell wall extension during stress conditions [7]

Methods

Results

Conclusion