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

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

JOURNAL=Frontiers in Plant Science

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.636663

DOI=10.3389/fpls.2021.636663

ISSN=1664-462X

ABSTRACT=<p>The biogenesis of root-knot nematode (<italic>Meloidogyne</italic> 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 <italic>ABAP1</italic> knockdown and overexpression in <italic>Arabidopsis thaliana</italic>. We detected <italic>ABAP1</italic> promoter activity and localized ABAP1 protein in galls during development, and its overexpression displayed significantly reduced gall sizes containing atypical giant cells. Profuse <italic>ABAP1</italic> expression also impaired gall induction and hindered nematode reproduction. Remarkably, <italic>ABAP1</italic> 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 <italic>ABAP1</italic> expression caused changes in expression patterns of genes involved in the cell division control as demonstrated by qRT-PCR. <italic>CDT1a</italic>, <italic>CDT1b</italic>, <italic>CDKA;1</italic>, and <italic>CYCB1;1</italic> mRNA levels were significantly increased in galls upon <italic>ABAP1</italic> overexpression, possibly contributing to the structural changes in galls during nematode infection. Overall, data obtained in galls reinforced the role of <italic>ABAP1</italic> controlling DNA replication and mitosis and, consequently, cell proliferation. <italic>ABAP1</italic> expression might likely take part of a highly ordered mechanism balancing of cell cycle control to prevent gall expansion. <italic>ABAP1</italic> expression might prevent galls to further expand, limiting excessive mitotic activity. Our data strongly suggest that <italic>ABAP1</italic> 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.</p>