Plant Diversity ›› 2019, Vol. 41 ›› Issue (05): 307-314.DOI: 10.1016/j.pld.2019.06.001

• Articles • Previous Articles     Next Articles

Cell number explains the intraspecific spur-length variation in an Aquilegia species

Zhi-Li Zhoua,b, Yuan-Wen Duana, Yan Luoc, Yong-Ping Yanga, Zhi-Qiang Zhangd   

  1. a Institute of Tibetan Plateau Research at Kunming, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, 650201, China;
    b University of Chinese Academy of Sciences, Beijing 100049, China;
    c Gardening and Horticulture Department, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, 666303, China;
    d Laboratory of Ecology and Evolutionary Biology, Yunnan University, Kunming, 650091, China
  • Received:2019-04-22 Revised:2019-06-06 Online:2019-10-25 Published:2019-11-21
  • Contact: Yong-Ping Yang,E-mail;Zhi-Qiang Zhang,E-mail
  • Supported by:
    We thank Dr. Wen Guo for field sampling. This work was financially supported by National Natural Science Foundation of China (31760104, 41461014, 31460040, and 31870183).

Abstract: Variations of nectar spur length allow pollinators to utilize resources in novel ways, leading to the different selective pressures on spurs and allowing taxa to diversify. However, the mechanisms underlying spur length variation remain unclear. Interspecific comparisons of spur length suggest that both cell division and anisotropic expansion could explain the changes of spur length, and that hormone-related genes contribute to the process of spur formation. In contrast, little is known about intraspecific spur length variation. In Aquilegia rockii, spur length varies strikingly, ranging from 1 mm to 18 mm. To examine the potential mechanisms underlying spur length variation in A. rockii, we observed cell morphology and analyzed RNA-seq of short- and long-spurred flowers. Scanning electron microscopy revealed that at two positions on spurs there were no differences in either cell density or cell anisotropy between short- and long-spurred flowers, suggesting that in A. rockii changes in cell number may explain variations in spur length. In addition, we screened transcriptomes of short- and long-spurred flowers for differentially expressed genes; this screen identified several genes linked to cell division (e.g., F-box, CDKB2-2, and LST8), a finding which is consistent with our analysis of the cellular morphology of spurs. However, we did not find any highly expressed genes involved in the hormone pathway in long-spurred flowers. In contrast to previous hypotheses that anisotropic cell expansion leads to interspecific spur variation in Aquilegia, our results suggest that cell number changes and related genes are mainly responsible for spur length variations of A. rockii. Furthermore, the underlying mechanisms of similar floral traits in morphology may be quite different, enriching our understanding of the mechanisms of flower diversity in angiosperms.

Key words: Aquilegia rockii, Cell number, Columbine, Floral polymorphism, Intraspecific variation, Nectar spur