Strigolactones might regulate ovule development after fertilization in Xanthoceras sorbifolium

Abstract

Abstract Background Strigolactones (SLs) were recently defined as a novel class of plant hormones that act as key regulators of diverse developmental processes and environmental responses. Much research has focused on SL biosynthesis and signaling in roots and shoots, but little is known about whether SLs are produced in early developing seeds and about their roles in ovule development after fertilization. Results The fertilized ovules and early developing pericarp in Xanthoceras sorbifolium produced minute amounts of two strigolactones: 5-deoxystrigol and strigol. Their content decreased in the plants with the addition of exogenous phosphate (Pi) compared to those without Pi treatment. Exogenous application of an SL analog (GR24) and a specific inhibitor of SL biosynthesis (TIS108) affected early seed development and fruit set. We identified a total of 69 putative Xanthoceras homologs of genes related to SL biological synthesis and signaling in the Xanthoceras genome. The expression of these genes in the ovules after fertilization was profiled using RNA-seq, resulting in the identification of 37 genes that were differentially expressed between the normally developing ovules and senescing ovules after fertilization. Transcriptome analysis also revealed that 12 putative invertase genes were actively expressed in normally developing ovules after fertilization. Hexoses (glucose and fructose) accumulated at high concentrations in normally developing ovules during syncytial endosperm development. In contrast, a low ratio of hexose and sucrose levels was detected in senescing ovules with a high strigolactone content. Virus-induced gene silencing (VIGS)-mediated XsD14 gene silencing increased hexose content in fertilized ovules and induced proliferation of endosperm free nuclei, thereby promoting early seed development and fruit set. Conclusion SLs are produced in early developing seeds and may play an important role in regulating ovule development after fertilization. The crosstalk between sugar and strigolactone signals may be an important part of a system that accurately regulates senescence of ovules after fertilization. This study is useful for understanding the mechanisms underlying ovule senescence, which will serve as a guide for genetic or chemical approaches to promote seed yield in Xanthoceras.