Lily (Lilium spp.) is an important horticultural crop, but its use is limited due to serious pollen contamination problems. There are many studies on pollen development in model plants, but few on flower crops such as lilies. Gibberellin (GA) is a large class of hormones and plays an important role in plant vegetative growth and reproductive development. GAMYB is a group of the R2R3-MYB family upregulated by gibberellin, and plays an important role in anther development. Here, we isolated a novel GAMYB, named LoMYB65, from lily, which was closely related to the AtMYB65 and AtMYB33 in Arabidopsis. Fluorescence quantitative PCR results showed that LoMYB65 was mainly expressed in lily anthers. LoMYB65 could be activated by 288 μmol · L⁻¹ GA₃ treatment and the LoMYB65 protein was located in the nucleus and cytoplasm, and had transactivation in yeast and tobacco leaf cells. The conserved motif within 226 amino acids of the C-terminal of LoMYB65 contributed to its transactivation. Overexpression of LoMYB65 caused dwarf phenotype, unnormal tapetum development, less seeds of siliques in transgenic Arabidopsis plants, the transgenic plants showed partly male sterile. Simultaneously, silencing of LoMYB65 with VIGS (Virus Induced Gene Silencing) in lily anthers caused unnormal pollen development and reduced the pollen amount. Overexpression of LoMYB65 in Arabidopsis and silencing of LoMYB65 in lily resulted in decreased pollen counts, so we speculate that LoMYB65 may be dose-dependent. Overall, these findings suggest that LoMYB65 may play an important role in anther development and pollen formation in lily. LoMYB65 may provide a useful candidate gene for pollenless breeding of lily.

Lily was grown worldwide as a fresh cutting flower because of its colorful petals, but its anther contained a large number of pollen grains that cause serious pollen contamination, however, pollen abortion can effectively reduce the level of pollen pollution. Our analysis aims to use cytological observation to detect the critical stage when pollen abortion occurs and to provide comprehensive gene expression information at the transcriptional level. The result showed that pollen abortion in ‘Little Kiss’ began at the mononuclear stage and the callose that covers the microspores failed to degenerate when young pollens were released from the tetrads. In addition, compared with the normally developed one, the tapetum of ‘Little Kiss’ degraded in advance while the degradation of callose was delayed. Furthermore, 103 differentially expressed genes (DEGs) related to the advance degeneration of tapetum cells and callose were found in the expression levels, including 22 transcription factors (TFs). In particular, two β-glucanase genes (endo-1,3(4)-β-glucanase, exo-β-glucanase) responsible for callose degeneration were significantly down-regulated. These results suggested that pollen abortion may occur at mononuclear stage and that early degeneration of tapetum cells resulted in a significant down-regulation of β-glucanase genes. As a result, the callose to cover microspores impedes the formation of pollen walls, which may possibly lead to pollen abortion.