Expression and Role of Biosynthetic, Transporter, Receptor, and Responsive Genes for Auxin Signaling during Clubroot Disease Development.

Arif Hasan Khan Robin,Rawnak Laila,Jong-In Park,Ill-Sup Nou,Hoy-Taek Kim,Gopal Saha

doi:10.3390/ijms21155554

Abstract

Auxins play a pivotal role in clubroot development caused by the obligate biotroph Plasmodiophora brassicae. In this study, we investigated the pattern of expression of 23 genes related to auxin biosynthesis, reception, and transport in Chinese cabbage (Brassica rapa) after inoculation with P. brassicae. The predicted proteins identified, based on the 23 selected auxin-related genes, were from protein kinase, receptor kinase, auxin responsive, auxin efflux carrier, transcriptional regulator, and the auxin-repressed protein family. These proteins differed in amino acids residue, molecular weights, isoelectric points, chromosomal location, and subcellular localization. Leaf and root tissues showed dynamic and organ-specific variation in expression of auxin-related genes. The BrGH3.3 gene, involved in auxin signaling, exhibited 84.4-fold increase in expression in root tissues compared to leaf tissues as an average of all samples. This gene accounted for 4.8-, 2.6-, and 5.1-fold higher expression at 3, 14, and 28 days post inoculation (dpi) in the inoculated root tissues compared to mock-treated roots. BrNIT1, an auxin signaling gene, and BrPIN1, an auxin transporter, were remarkably induced during both cortex infection at 14 dpi and gall formation at 28 dpi. BrDCK1, an auxin receptor, was upregulated during cortex infection at 14 dpi. The BrLAX1 gene, associated with root hair development, was induced at 1 dpi in infected roots, indicating its importance in primary infection. More interestingly, a significantly higher expression of BrARP1, an auxin-repressed gene, at both the primary and secondary phases of infection indicated a dynamic response of the host plant towards its resistance against P. brassicae. The results of this study improve our current understanding of the role of auxin-related genes in clubroot disease development.

Highlights

Clubroot, a serious disease of Brassicaceae family members throughout the world, is caused by an obligate biotroph Plasmodiophora brassicae Woronin
BrDCK1 and BrARG10like genes exhibited 28.2- and 10.9-fold higher expression in root tissues compared to leaf tissues, respectively (Figure 2)
The BrGH3.3, BrDCK1, and BrARG10like genes were comparatively highly expressed by 84.4, 28.2, and 10.9-fold, respectively, in root tissues compared to leaf tissues, indicating that these three genes are important in auxin-mediated root development (Figure 2)

Summary

Introduction

A serious disease of Brassicaceae family members throughout the world, is caused by an obligate biotroph Plasmodiophora brassicae Woronin. P. brassicae completes its life cycle in two phases: a primary phase which is mainly confined to root hairs of the host plants and a secondary phase that takes place in the cortex and the stele of the hypocotyl and roots of the infected plants, leading to cell hypertrophy (cell division) and hyperplasia (cell elongation) and resulting in “gall” or “club”. Cell division was reported to start from 4 days after inoculation (dai), which continues throughout the secondary cycle of infection, resulting in hypertrophied cells large in size that harbor secondary plasmodia and resting spores [5]. These resting spores are highly persistent, and they may remain infectious up to 15 years in soil [6]. In the progression of a clubroot disease, pathogens can efficiently alter the auxin responses [8]

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Discussion

Conclusion