Deciphering the Molecular Mechanisms That Control Ovule Development in Pomegranate

Plant seed number depends on ovule number initiated within the carpels, and it serves as a primary factor shaping fruit yield. Pomegranate trees exhibit bisexual flowers and functional male flowers. Pomegranate have anatropous ovules which are bitegmic and crassinucellate. Bisexual flowers possess the fertile pistil, while functional male flowers have abnormally developed ovules, a small ovary with few chambers, and a short style. The formation of functional male flowers is due to abnormal and stagnant development of ovule integument. Ovule number directly determines the yield of pomegranate seeds. Recent studies have highlighted the molecular mechanisms through which ovule-related genes regulate pomegranate ovule development. Pomegranate PgCRC and PgINO genes positively regulate the increase in the number of ovules, and PgBEL1 to synergistically regulate seed development. PgAGL11 (the SEEDSTICK orthologous gene) promotes ovule development in transgenic Arabidopsis. PgSEP protein can bridge interactions among PgBEL1, PgSTK and PgAG, which regulate ovule development. At the level of post-transcriptional regulation, PgmiRNA167, PgmiRNA164 and PgmiRNA160 are differentially expressed during pomegranate flower development, and PgmiR166a interacts with its target genes to affect ovule development. This review summarizes the key regulators of ovule development and their molecular pathways, integrating these interactions into a model that describes pomegranate ovule development.