Mildew resistance locus O (MLO) is a plant-specific gene family that plays an important role in the growth and development of plants and their interactions with the environment.  However, the available information on this gene family in pear is limited.  Here, 24 PbrMLO genes were identified and divided into five subfamilies (I, II, III, IV and V).  Whole-genome duplication (WGD) and dispersed duplication contributed to the expansion of the PbrMLO family.  In addition, gene expression analysis revealed that PbrMLO genes were distributed in various pear tissues, suggesting their diverse functions.  We selected PbrMLO23 for further functional analysis.  Expression profile analysis by qRT-PCR showed that PbrMLO23 was highly expressed in pollen.  Subcellular localization analysis showed that PbrMLO23 was located on the plasma membrane.  When the expression level of PbrMLO23 was knocked down by using antisense oligonucleotides, pollen tube lengths increased, indicating that PbrMLO23 plays a functional role in inhibiting pollen tube growth.  In summary, these results provide evolutionary insight into PbrMLO and its functional characteristics and lay a foundation for further analysis of the functions of PbrMLO members in pear.

 

Soil waterlogging is a major environmental stress that suppresses the growth and productivity of rapeseed (Brassica napus L.).  Natural genetic variations in waterlogging tolerance (WT) were observed but no QTL mapping has been done for WT related traits in rapeseed. In this study, QTL associated with three WT related traits including relative root length (RRL), relative hypocotyl length (RHL) and relative fresh weight (RFW) were dissected using a set of reciprocal introgression lines (ILs) derived from the cross GH01×ZS9, which showed significant difference in WT.  Genotyping-by-sequencing (GBS) of the populations were performed, totally 1 468 and 1 450 binned SNPs were identified for GIL (GH01 as the recurrent parent) and ZIL (ZS9 as the recurrent parent) population, respectively.  A total of 66 distinct QTLs for WT at the seedling establishment stage including 31 for RRL, 17 for RHL and 18 for RFW were detected.  Among the 66 QTLs, 20 (29.4%) QTLs were detected in both genetic backgrounds and then they were integrated into six QTL clusters, which can be targeted in rapeseed breeding for improvement of WT through marker-assisted selection (MAS).  Based on the physical positions of SNPs and the functional annotation of the Arabidopsis thaliana genome, 56 genes within the six QTL cluster regions were selected as preliminary candidate genes, then the resequencing and transcriptome information about parents were applied to narrow the extent of candidate genes.  Twelve genes were determined as candidates for the six QTL clusters, some of them involved in RNA/protein degradation, most of them involved in oxidation-reduction process.  These findings provided genetic resources, candidate genes to address the urgent demand of improving WT in rapeseed breeding.