Characterization of a Common S Haplotype BnS-6 in the Self-Incompatibility of Brassica napus

Zhiquan Liu,Bing Li,Bin Yi,Chaozhi Ma,Yong Yang,Jinxiong Shen,Changbin Gao,Jinxing Tu,Tingdong Fu,Jing Wen,Cheng Dai

doi:10.3390/plants10102186

Abstract

Self-incompatibility (SI) is a pollen-stigma recognition system controlled by a single and highly polymorphic genetic locus known as the S-locus. The S-locus exists in all Brassica napus (B. napus, AACC), but natural B. napus accessions are self-compatible. About 100 and 50 S haplotypes exist in Brassica rapa (AA) and Brassica oleracea (CC), respectively. However, S haplotypes have not been detected in B. napus populations. In this study, we detected the S haplotype distribution in B. napus and ascertained the function of a common S haplotype BnS-6 through genetic transformation. BnS-1/BnS-6 and BnS-7/BnS-6 were the main S haplotypes in 523 B. napus cultivars and inbred lines. The expression of SRK in different S haplotypes was normal (the expression of SCR in the A subgenome affected the SI phenotype) while the expression of BnSCR-6 in the C subgenome had no correlation with the SI phenotype in B. napus. The BnSCR-6 protein in BnSCR-6 overexpressed lines was functional, but the self-compatibility of overexpressed lines did not change. The low expression of BnSCR-6 could be a reason for the inactivation of BnS-6 in the SI response of B. napus. This study lays a foundation for research on the self-compatibility mechanism and the SI-related breeding in B. napus.

Highlights

Self-incompatibility (SI), which is a genetic mechanism that helps to avoid inbreeding depression and promotes outcrossing by rejecting self-pollination, occurs in approximately40% of flowering plant species [1,2]
In Brassicaceae, the S-locus mainly includes the pollen determinant of SI, S-locus cysteine-rich protein (SCR)/S-locus protein 11 (SP11) [4,5], and the stigma determinant of SI, a papilla cell localized in membrane-anchored Ser/Thr kinase (S-locus receptor kinase gene, SRK) [6,7]
Based on the dominance and nucleotide sequences of SCR and SRK in Brassica, S haplotypes can be divided into two classes: Class I and II [16,17]

Summary

Introduction

Self-incompatibility (SI), which is a genetic mechanism that helps to avoid inbreeding depression and promotes outcrossing by rejecting self-pollination, occurs in approximately40% of flowering plant species [1,2]. SI responses in many plant species [3]. When the pollen lands on the stigma of the same S haplotype, specificity recognition between SCR and SRK will trigger the SI response [7,12]. This S haplotype-specific receptor–ligand interaction results in the activation of a polleninhibitory signaling pathway upon self-pollination [13]. There are approximately 100 known S haplotypes in B. rapa and 50 S haplotypes in B. oleracea that regulate SI response, respectively [14,15]. Further studies have indicated that the dominant effect of different SCR genes is regulated by SMI (SCR-methylation-inducer) and SMI2 (SCR-methylationinducer 2) [19,20]

Methods

Results

Conclusion