Abstract
Seed weight is an important target trait in pomegranate breeding and culture. Expansins act by loosening plant cell walls and cellulosic materials, permitting turgor-driven cell enlargement. However, the role of expansin genes (EXPs) in pomegranate seed weight remains elusive. A total of 29 PgrEXPs were identified in the 'Dabenzi' genome. These genes were classified into four subfamilies and 14 subgroups, including 22 PgrEXPAs, 5 PgrEXPBs, 1 PgrEXPLA, and 1 PgrEXPLB. Transcriptome analysis of PgrEXPs in different tissues (root, leaf, flower, peel, and seed testa) in 'Dabenzi', and the seed testa of the hard-seeded pomegranate cultivar 'Dabenzi' and soft-seeded cultivar 'Tunisia' at three development stages showed that three PgrEXPs (PgrEXPA11, PgrEXPA22, PgrEXPA6) were highly expressed throughout seed development, especially in the sarcotesta. SNP/Indel markers of these PgrEXPs were developed and used to genotype 101 pomegranate accessions. The association of polymorphic PgrEXPs with seed weight-related traits (100-seed weight, 100-kernel weight, 100-sarcotesta weight, and the percentage of 100-sarcotesta to 100-seed weight) were analyzed. PgrEXP22 was significantly associated with 100-seed weight and 100-sarcotesta weight and is a likely candidate for regulating seed weight and sarcotesta development in particular. This study provides an effective tool for the genetic improvement of seed weight in pomegranate breeding programs.