Molecular Network for Regulation of Ovule Number in Plants

Abstract

In seed-bearing plants, the ovule (“small egg”) is the organ within the gynoecium that develops into a seed after fertilization. The gynoecium located in the inner compartment of the flower turns into a fruit. The number of ovules in the ovary determines the upper limit or the potential of seed number per fruit in plants, greatly affecting the final seed yield. Ovule number is an important adaptive characteristics for plant evolution and an agronomic trait for crop improvement. Therefore, understanding the mechanism and pathways of ovule number regulation becomes a significant research aspect in plant science. This review summarizes the ovule number regulators and their regulatory mechanisms and pathways. Specially, we construct the first integrated molecular network for ovule number regulation, in which phytohormones played a central role, followed by transcription factors, enzymes, other protein and micro-RNA. Of them, AUX, BR and CK are positive regulator of ovule number, whereas GA acts negatively on it. Interestingly, many ovule number regulators have conserved functions across several plant taxa, which should be the targets of genetic improvement via breeding or gene editing. Many ovule number regulators identified to date are involved in the diverse biological process, such as ovule primordia formation, ovule initiation, patterning, and morphogenesis. The relations between ovule number and related characteristics/traits especially of gynoecium/fruit size, ovule fertility, and final seed number, as well as upcoming research questions, are also discussed. In summary, this review provides a general overview of the present finding in ovule number regulation, which represents a more comprehensive and further cognition on it.

Ovule initiation: the essential step controlling offspring number in Arabidopsis

“…Ovule number might be considered to reflect ovule initiation; however, their properties are not exactly the same. Previous work has also identified several hormonal signals that regulate placenta formation and ovule number, which are similar to weak mutants of development‐related genes (Bencivenga et al, 2012; Cucinotta et al, 2014; Marsch‐Martínez and de Folter, 2016; Deb et al, 2018; Cucinotta et al, 2020; Qadir et al, 2021; Yang and Tucker, 2021); and other hormonal signals involved in ovule number regulation but not in placenta formation (Bartrina et al, 2011; Huang et al, 2013; Gómez et al, 2018), these studies provide further evidence that influencing ovule number does not equate to disturbing ovule initiation.…”

“…Research into ovule development has mainly focused on the middle and late stages (Drews and Koltunow, 2011; Hater et al, 2020; Jia et al, 2020; Ma et al, 2021; Aslam et al, 2022). Hormonal regulation of ovule initiation and ovule number has been well characterized (Cucinotta et al, 2014; Marsch‐Martínez and de Folter, 2016; Deb et al, 2018; Cucinotta et al, 2020; Barro‐Trastoy et al, 2020b; Qadir et al, 2021; Yang and Tucker, 2021). The initiation process of multiple ovules in the same placenta was reported recently, providing a new field of research into ovule initiation and determination of ovule number (Yu et al, 2020; Hu et al, 2022b).…”

“…Other hormones, such as cytokinin (CK), brassinosteroid (BR), and gibberellin (GA), are also involved in regulating ovule initiation and contribute to gynoecium size and ovule number (Bartrina et al, 2011; Huang et al, 2013; Gómez et al, 2018). These hormones can work both independently and through crosstalk with each other to influence ovule initiation (Cucinotta et al, 2014; Marsch‐Martínez and de Folter, 2016; Deb et al, 2018; Cucinotta et al, 2020; Qadir et al, 2021; Yang and Tucker, 2021). The molecular mechanisms by which individual hormones regulate ovule initiation, as well as some crosstalk between hormones, have been well summarized in previous reviews (Cucinotta et al, 2014; Cucinotta et al, 2020; Barro‐Trastoy et al, 2020b; Qadir et al, 2021; Yang and Tucker, 2021).…”

“…These hormones can work both independently and through crosstalk with each other to influence ovule initiation (Cucinotta et al, 2014; Marsch‐Martínez and de Folter, 2016; Deb et al, 2018; Cucinotta et al, 2020; Qadir et al, 2021; Yang and Tucker, 2021). The molecular mechanisms by which individual hormones regulate ovule initiation, as well as some crosstalk between hormones, have been well summarized in previous reviews (Cucinotta et al, 2014; Cucinotta et al, 2020; Barro‐Trastoy et al, 2020b; Qadir et al, 2021; Yang and Tucker, 2021). Here, we briefly introduce the individual functions of auxin, CK, BR, and GA in ovule initiation, and discuss some very recent progress in understanding auxin regulation of asynchronous ovule initiation and the integration of different hormones regulating ovule initiation (Figure 2).…”

Editorial: Functional Genomics in Plant Breeding 2.0

“…In seed-bearing plants, the number of ovules determines the potential of seed number per fruit, significantly affecting the final seed yield; therefore, it is a significant research aspect of plant science. Hence, Qadir et al [16] summarized the ovule number's regulators, regulatory agencies, pathways, and molecular networks. This review also gives suggestions for the molecular improvement of ovule numbers, which will be very useful for plant breeders.…”