The Armadillo BTB Protein ABAP1 Is a Crucial Player in DNA Replication and Transcription of Nematode-Induced Galls.

Danila Cabral,Isabela Tristan Lourenço-Tessutti,Bruno Paes De Melo,Adriana S Hemerly,Kércya Maria Simões De Siqueira,Luciana Obicci,Maria Fatima Grossi-De-Sa,Helkin Forero Ballesteros,Janice De Almeida Engler

doi:10.3389/fpls.2021.636663

Abstract

The biogenesis of root-knot nematode (Meloidogyne spp.)-induced galls requires the hyperactivation of the cell cycle with controlled balance of mitotic and endocycle programs to keep its homeostasis. To better understand gall functioning and to develop new control strategies for this pest, it is essential to find out how the plant host cell cycle programs are responding and integrated during the nematode-induced gall formation. This work investigated the spatial localization of a number of gene transcripts involved in the pre-replication complex during DNA replication in galls and report their akin colocation with the cell cycle S-phase regulator Armadillo BTB Arabidopsis Protein 1 (ABAP1). ABAP1 is a negative regulator of pre-replication complex controlling DNA replication of genes involved in control of cell division and proliferation; therefore, its function has been investigated during gall ontogenesis. Functional analysis was performed upon ABAP1 knockdown and overexpression in Arabidopsis thaliana. We detected ABAP1 promoter activity and localized ABAP1 protein in galls during development, and its overexpression displayed significantly reduced gall sizes containing atypical giant cells. Profuse ABAP1 expression also impaired gall induction and hindered nematode reproduction. Remarkably, ABAP1 knockdown likewise negatively affected gall and nematode development, suggesting its involvement in the feeding site homeostasis. Microscopy analysis of cleared and nuclei-stained whole galls revealed that ABAP1 accumulation resulted in aberrant giant cells displaying interconnected nuclei filled with enlarged heterochromatic regions. Also, imbalanced ABAP1 expression caused changes in expression patterns of genes involved in the cell division control as demonstrated by qRT-PCR. CDT1a, CDT1b, CDKA;1, and CYCB1;1 mRNA levels were significantly increased in galls upon ABAP1 overexpression, possibly contributing to the structural changes in galls during nematode infection. Overall, data obtained in galls reinforced the role of ABAP1 controlling DNA replication and mitosis and, consequently, cell proliferation. ABAP1 expression might likely take part of a highly ordered mechanism balancing of cell cycle control to prevent gall expansion. ABAP1 expression might prevent galls to further expand, limiting excessive mitotic activity. Our data strongly suggest that ABAP1 as a unique plant gene is an essential component for cell cycle regulation throughout gall development during nematode infection and is required for feeding site homeostasis.

Highlights

Nematode-induced galls in plant roots are unusual tumorlike structures formed as a consequence of vascular tissue cell dedifferentiation and proliferation strongly engaging cell cycle reprogramming
Our results provide strong evidences that galls induced by parasitic root-knot nematodes usurp the pre-replication complex (pre-RC) of plant hosts in order to hyperactivate their cell cycle (Figure 9)
Even when mitotic activity ceases in galls, transcription of pre-RC components here studied remained during DNA replication through the endocycle, suggesting the use of a common regulation of the DNA replication machinery in both phases

Summary

Introduction

Nematode-induced galls in plant roots are unusual tumorlike structures formed as a consequence of vascular tissue cell dedifferentiation and proliferation strongly engaging cell cycle reprogramming. Nematode feeding sites (NFS) are likely induced by nematode secretions and hold giant cells (GCs) used as the only nourishing source for the nematode (Vieira and Gleason, 2019). These giant-feeding cells are surrounded by neighboring cells (NCs) undergoing cycles of asymmetric cell divisions during initial gall genesis and require the activation and balance of mitotic and endocycle phases (de Almeida-Engler et al, 1999; de Almeida Engler and Gheysen, 2013; Vieira et al, 2013). The passage across successive cell cycle phases is controlled by cyclin-dependent kinases (CDKA; in Arabidopsis) that are activated upon binding to regulatory proteins such as mitotic cyclins, and by phosphorylation (Jeffrey et al, 1995; Nigg, 1995; Russo et al, 1996)

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