Abstract
ABSTRACTPlant ovule initiation determines the maximum of ovule number and has a great impact on the seed number per fruit. The detailed processes of ovule initiation have not been accurately described, although two connected processes, gynoecium and ovule development, have been investigated. Here, we report that ovules initiate asynchronously. The first group of ovule primordia grows out, the placenta elongates, the boundaries of existing ovules enlarge and a new group of primordia initiates from the boundaries. The expression pattern of different marker genes during ovule development illustrates that this asynchronicity continues throughout whole ovule development. PIN-FORMED1 polar distribution and auxin response maxima correlate with ovule primordia asynchronous initiation. We have established computational modeling to show how auxin dynamics influence ovule primordia initiation. Brassinosteroid signaling positively regulates ovule number by promoting placentae size and ovule primordia initiation through strengthening auxin response. Transcriptomic analysis demonstrates numerous known regulators of ovule development and hormone signaling, and many new genes are identified that are involved in ovule development. Taken together, our results illustrate that the ovule primordia initiate asynchronously and the hormone signals are involved in the asynchrony.
Highlights
The formation of lateral organ primordia is a significant event in the growth and development of plants and animals
If we consider the ovule primordium as a cylinder protruding from the placenta, there are at least three different shapes of ovule primordia at stage 9 based on the height and basal diameter of the cylinder
A second group of auxin maxima is formed, which induces the auxin response and the initiation of the second group of ovule primordia (Fig. 6D; Movie 1). These results suggest that new ovule primordia initiation requires PIN1 polarity and the formation of localized auxin maxima, and that ovule primordia initiate in different groups tightly accompanied by the auxin response
Summary
The formation of lateral organ primordia is a significant event in the growth and development of plants and animals. Plant lateral organ primordia include the primordia of lateral root, leaf, and flower (Steeves and Sussex, 1989; Benková et al, 2003; Heisler et al, 2005), and ovule primordia initiation could be considered as another lateral organ initiation. Handling Editor: Ykä Helariutta Received 3 September 2020; Accepted 6 November 2020 event (Cucinotta et al, 2014). The innermost whorl, i.e. the female reproductive organs, consists of two fused carpels that develop into four placentae (Bowman et al, 1991)
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