Abstract
Lily (Lilium spp.) is an important commercial flower crop, but its market popularity and applications are adversely affected by severe pollen pollution. Many studies have examined pollen development in model plants, but few studies have been conducted on flower crops such as lily. GAMYBs are a class of R2R3-MYB transcription factors and play important roles in plant development and biotic resistance; their functions vary in different pathways, and many of them are involved in anther development. However, their function and regulatory role in lily remain unclear. Here, the GAMYB homolog LoMYB33 was isolated and identified from lily. The open reading frame of LoMYB33 was 1620 bp and encoded a protein with 539 amino acids localized in the nucleus and cytoplasm. Protein sequence alignment showed that LoMYB33 contained a conserved R2R3 domain and three BOX motifs (BOX1, BOX2, and BOX3), which were unique to the GAMYB family. LoMYB33 had transcriptional activation activity, and its transactivation domain was located within 90 amino acids of the C-terminal. LoMYB33 was highly expressed during the late stages of anther development, especially in pollen. Analysis of the promoter activity of LoMYB33 in transgenic Arabidopsis revealed that the LoMYB33 promoter was highly activated in the pollen of stage 12 to 13 flowers. Overexpression of LoMYB33 in Arabidopsis significantly retarded growth; the excess accumulation of LoMYB33 also negatively affected normal anther development, which generated fewer pollen grains and resulted in partial male sterility in transgenic plants. Silencing of LoMYB33 in lily also greatly decreased the amount of pollen. Overall, our results suggested that LoMYB33 might play an important role in the anther development and pollen formation of lily.
Highlights
Pollen is required for sexual reproduction in plants (Aizen and Harder, 2007)
Phylogenetic analysis with 124 MYB family transcription factors (TFs) from Arabidopsis indicated that LoMYB33 was closely related to AtMYB33 and AtMYB65 (Supplementary Figure 1), both of which are GAMYB family members (Millar and Gubler, 2005; Tsuji et al, 2006; Li et al, 2016)
Multiple protein alignment with the amino acid sequences of homologs from E. guineensis, O. sativa, Arabidopsis, R. chinensis, Zea mays, Glycine max, Hordeum vulgare, Triticum aestivum, Solanum lycopersicum, and Cucumis sativus showed that LoMYB33 contained the classical R2R3 domain of the R2R3-MYB family (Figure 1B), indicating that it belonged to the R2R3-MYB family
Summary
Pollen is required for sexual reproduction in plants (Aizen and Harder, 2007). Normal pollen development is essential for ensuring the high yield and quality of crops and fruits, but deleterious effects are often inevitable. Gibberellins (GAs) are a major group of hormones in plants that play an essential role in plant vegetative growth and reproductive development (Hedden, 2001). In 1995, GAMYBs were first reported in barley aleurone cells, and they were shown to be up-regulated by gibberellin (GA) and activated GA-regulated genes (Gubler et al, 1995). GAMYBs play important roles in flower induction and flowering regulation. GAMYBs have been reported to regulate anther development in a variety of plants (Kaneko et al, 2004). Both AtMYB33 and AtMYB65 are GAMYB family members in Arabidopsis, which function redundantly to regulate anther development and pollen formation (Millar and Gubler, 2005). Rice gamyb mutants are sterile because the anthers are poorly developed and lack pollen (Aya et al, 2009)
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