Abstract
Chrysanthemum (Chrysanthemum morifolium (Ramat.) Kitamura) plants have great ornamental value, but their flowers can also be a source of pollen contamination. Previously, morphological and cytological studies have shown that anthers of some chrysanthemum cultivars such as ‘Qx-115′ fail to dehisce, although the underlying mechanism is largely unknown. In this study, we investigated the molecular basis of anther indehiscence in chrysanthemum via transcriptome analysis of a dehiscent cultivar (‘Qx-097′) and an indehiscent cultivar (‘Qx-115′). We also measured related physiological indicators during and preceding the period of anther dehiscence. Our results showed a difference in pectinase accumulation and activity between the two cultivars during dehiscence. Detection of de-esterified pectin and highly esterified pectin in anthers during the period preceding anther dehiscence using LM19 and LM20 monoclonal antibodies showed that both forms of pectin were absent in the stomium region of ‘Qx-097′ anthers but were abundant in that of ‘Qx-115′ anthers. Analysis of transcriptome data revealed a significant difference in the expression levels of two transcription factor-encoding genes, CmLOB27 and CmERF72, between ‘Qx-097′ and ‘Qx-115′ during anther development. Transient overexpression of CmLOB27 and CmERF72 separately in tobacco leaves promoted pectinase biosynthesis. We conclude that CmLOB27 and CmERF72 are involved in the synthesis of pectinase, which promotes the degradation of pectin. Our results lay a foundation for further investigation of the role of CmLOB27 and CmERF72 transcription factors in the process of anther dehiscence in chrysanthemum.
Highlights
Chrysanthemum (Chrysanthemum morifolium (Ramat.) Kitamura) originates from China, where it is one of the 10 most beloved traditional flowers, and is among the world’s most popular cut flowers [1]
At the crucial stage of anther dehiscence, in the ‘Qx-097’ sample (Qx-097-2; Figure 2B), the anther septum was completely degraded, and the cells in the stomium region were in the process of degradation
The ‘Qx-097-2’ anthers showed a crack, and pollen grains released from this crack could be observed (Figure 2B)
Summary
Chrysanthemum (Chrysanthemum morifolium (Ramat.) Kitamura) originates from China, where it is one of the 10 most beloved traditional flowers, and is among the world’s most popular cut flowers [1]. Chrysanthemum flowers have a single capitulum/inflorescence which bears multiple bisexual tubular flowers and female ray flowers; all of the bisexual tubular flowers release pollen grains after anther dehiscence, it may cause serious pollen contamination. Pollen contamination significantly reduces the ornamental value of chrysanthemum, quickly shortens its shelf life, and elicits severe allergic reactions in some people, those allergic to pollen [2,3]. Manual removal of anthers can ameliorate the pollen contamination of cut flowers; this method is not feasible in chrysanthemum. Manual removal of anthers is time-consuming and laborious, and causes chrysanthemum to lose its ornamental value. Pollen contamination due to chrysanthemum flowers is a major problem in the cut flower industry and should be urgently resolved. Breeding of male sterile lines with anther indehiscence or pollen abortion phenotype could be used to reduce or eliminate pollen pollution due to chrysanthemum flowers
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