Abstract
The plant hormone gibberellin (GA) is known to regulate elongating growth, seed germination, and the initiation of flower bud formation, and it has been postulated that GAs originally had functions in reproductive processes. Studies on the mechanism of induction of flowering by GA have been performed in Arabidopsis and other model plants. In coniferous trees, reproductive organ induction by GAs is known to occur, but there are few reports on the molecular mechanism in this system. To clarify the gene expression dynamics of the GA induction of the male strobilus in Cryptomeria japonica, we performed comprehensive gene expression analysis using a microarray. A GA-treated group and a nontreated group were allowed to set, and individual trees were sampled over a 6-week time course. A total of 881 genes exhibiting changed expression was identified. In the GA-treated group, genes related to ‘stress response’ and to ‘cell wall’ were initially enriched, and genes related to ‘transcription’ and ‘transcription factor activity’ were enriched at later stages. This analysis also clarified the dynamics of the expression of genes related to GA signaling transduction following GA treatment, permitting us to compare and contrast with the expression dynamics of genes implicated in signal transduction responses to other plant hormones. These results suggested that various plant hormones have complex influences on the male strobilus induction. Additionally, principal component analysis (PCA) using expression patterns of the genes that exhibited sequence similarity with flower bud or floral organ formation-related genes of Arabidopsis was performed. PCA suggested that gene expression leading to male strobilus formation in C. japonica became conspicuous within one week of GA treatment. Together, these findings help to clarify the evolution of the mechanism of induction of reproductive organs by GA.
Highlights
Gibberellins (GAs), a class of terpenoid plant hormones, regulate various important plant physiological processes, such as plant elongation, seed germination, and floral initiation [1,2].The endogenous active GA4 has been detected in the Lycopsida (Selaginella moellendorffii) but not in mosses (Physcomitrella patens) [3,4,5]
We examined changes in the expression patterns of genes associated with the GA signaling pathway, other plant hormone signaling pathways, or flowering in other species, aiming at providing insights into GA functional mechanisms in male strobilus induction in C. japonica
Male strobili of C. japonica were induced by GA3 spraying onto the shoots
Summary
Gibberellins (GAs), a class of terpenoid plant hormones, regulate various important plant physiological processes, such as plant elongation, seed germination, and floral initiation [1,2].The endogenous active GA4 has been detected in the Lycopsida (Selaginella moellendorffii) but not in mosses (Physcomitrella patens) [3,4,5]. Gibberellins (GAs), a class of terpenoid plant hormones, regulate various important plant physiological processes, such as plant elongation, seed germination, and floral initiation [1,2]. It is thought that GA signaling was acquired in the vascular plant. GAs are involved in microspore formation and sex determination, and GAs are inferred to have originally functioned in reproductive processes [7,8]. Studies of the model plant Arabidopsis thaliana identified six flowering pathways, known as age, autonomous, vernalization, photoperiod, temperature, and GA [9,10,11,12,13,14,15,16]. GA-mediated floral transitions in angiosperms have been the subject of multiple studies performed in model plants, including A. thaliana [9,15,17,18]
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