# Genome-Wide Identification of the SPP/SPPL Gene Family and BnaSPPL4 Regulating Male Fertility in Rapeseed (Brassica napus L.)

## TL;DR

This study identifies 26 SPP/SPPL genes in rapeseed and finds that BnaSPPL4 is crucial for male fertility, as its silencing leads to male sterility.

## Contribution

The first report on the role of SPP/SPPL genes in rapeseed, specifically identifying BnaSPPL4 as a regulator of male fertility.

## Key findings

- 26 SPP/SPPL genes were identified and categorized into three groups in rapeseed.
- BnaSPPL4 silencing causes male sterility due to microspore dysplasia in the mononucleate stage.
- SPP/SPPL genes are under strong purifying selection and are distributed across 17 chromosomes.

## Abstract

Signal peptide peptidase (SPP) and its homologs, signal peptide peptidase-like (SPPL) proteases, are members of the GxGD-type aspartyl protease family, which is widespread in plants and animals and is a class of transmembrane proteins with significant biological functions. SPP/SPPLs have been identified; however, the functions of SPP/SPPL in rapeseed (Brassica napus L.) have not been reported. In this study, 26 SPP/SPPLs were identified in rapeseed and categorized into three groups: SPP, SPPL2, and SPPL3. These members mainly contained the Peptidase_A22 and PA domains, which were distributed on 17 out of 19 chromosomes. Evolutionary analyses indicated that BnaSPP/SPPLs evolved with a large number of whole-genome duplication (WGD) events and strong purifying selection. Members are widely expressed and play a key role in the growth and development of rapeseed. The regulation of rapeseed pollen fertility by the BnaSPPL4 gene was further validated through experiments based on bioinformatics analysis, concluding that BnaSPPL4 silencing causes male sterility. Cytological observation showed that male infertility caused by loss of BnaSPPL4 gene function occurs late in the mononucleate stage due to microspore dysplasia.