Comprehensive analysis of polygalacturonase family highlights candidate genes related to pollen development and male fertility in wheat (Triticum aestivum L.)

Abstract

Background: Polygalacturonase (PG) belongs to a large family of hydrolases with important functions in cell separation during plant growth and development via the degradation of pectin. The specific expression of PG genes in anthers may be significant for male sterility research and hybrid wheat breeding, but it has not been characterized in wheat (Triticum aestivum L.). Results: We systematically studied the PG gene family using the latest published wheat reference genomic information. In total, 113 wheat PG genes were identified and renamed as TaPG01–113 based on their chromosomal positions. The PG genes are unequally distributed on 21 chromosomes and classified according to six categories from A–F. Analysis of the gene structures and conserved motifs demonstrated that the Class C and D TaPGs have relatively short gene sequences and a small number of introns. Class E TaPGs are the least conserved and lack conserved domain III. Polyploidy and segmental duplications in wheat were mainly responsible for the expansion of the wheat PG gene family. Predictions of cis-elements indicate that TaPGs have a wide range of functions, including the responses to light, hypothermia, anaerobic conditions, and hormonal stimulation, as well as being involved in meristematic tissue expression. RNA-seq showed that TaPGs have specific temporal and spatial expression characteristics. Twelve spike-specific TaPGs were screened using RNA-seq data and verified by qRT-PCR in the sterile and fertile anthers of thermo-sensitive male-sterile wheat. Four important candidate genes were identified as involved in the male fertility determination process. In fertile anthers, TaPG09 may be involved in the separation of pollen. TaPG87 and TaPG95 could play important roles in anther dehiscence. TaPG93 may be related to pollen development and pollen tube elongation. Conclusions: We analyzed the wheat PG gene family and identified four important TaPGs with differential expression levels in the wheat fertility conversion process. Our findings may facilitate functional investigations of the wheat PG gene family and provide new insights into the fertility conversion mechanism in male-sterile wheat.