Structural Maintenance of Chromosomes 5/6 Complex Is Necessary for Tetraploid Genome Stability in Arabidopsis thaliana.

Fen Yang,Joanna Majka,Nadia Fernández Jiménez,Mónica Pradillo,Ales Pecinka

doi:10.3389/fpls.2021.748252

Abstract

Polyploidization is a common phenomenon in the evolution of flowering plants. However, only a few genes controlling polyploid genome stability, fitness, and reproductive success are known. Here, we studied the effects of loss-of-function mutations in NSE2 and NSE4A subunits of the Structural Maintenance of Chromosomes 5/6 (SMC5/6) complex in autotetraploid Arabidopsis thaliana plants. The diploid nse2 and nse4a plants show partially reduced fertility and produce about 10% triploid offspring with two paternal and one maternal genome copies. In contrast, the autotetraploid nse2 and nse4a plants were almost sterile and produced hexaploid and aneuploid progeny with the extra genome copies or chromosomes coming from both parents. In addition, tetraploid mutants had more severe meiotic defects, possibly due to the presence of four homologous chromosomes instead of two. Overall, our study suggests that the SMC5/6 complex is an important player in the maintenance of tetraploid genome stability and that autotetraploid Arabidopsis plants have a generally higher frequency of but also higher tolerance for aneuploidy compared to diploids.

Highlights

Maintenance of genome stability is essential for ensuring plant growth, fertility, and proper genomic constitution of the offspring (Roy, 2014; Hu et al, 2016)
We included tetraploid nse4a2 (4x nse4a-2) because NSE4A is another subunit of Structural Maintenance of Chromosomes 5/6 (SMC5/6) complex whose loss-of-function plants have fertility defects (Díaz et al, 2019)
We analyzed the effects of polyploidy on the genome stability and reproductive success in the background of autotetraploid Arabidopsis SMC5/6 complex deficient mutants

Summary

Introduction

Maintenance of genome stability is essential for ensuring plant growth, fertility, and proper genomic constitution of the offspring (Roy, 2014; Hu et al, 2016). The core part of the complex consists of SMC5 and SMC6 protein heterodimer, where the subunits are attached via their hinge domains. SMC6 has two partially functionally redundant paralogs in Arabidopsis. Both play roles under ambient conditions, but only SMC6B takes place in DNA damage repair (Watanabe et al, 2009; Yan et al, 2013; Zou et al, 2021). While NSE1 and NSE3 are single-copy genes in Arabidopsis, there are two NSE4 paralogs (NSE4A and NSE4B) that show distinct expression patterns and functions (Díaz et al, 2019). Plant-specific SMC5/6 subunits ARABIDOPSIS SNI1 ASSOCIATED PROTEIN 1 (ASAP1) and SUPPRESSOR OF NPR1-1; INDUCIBLE 1 (SNI1) have been described (Yan et al, 2013). ASAP1 and SNI1 were proposed to be functionally homologous to the yeast SMC5/6 complex chromatin-loader subunits NSE5 and NSE6

Methods

Results

Conclusion