Abstract
Although four maturity genes, E1 to E4, in soybean have been successfully cloned, their functional mechanisms and the regulatory network of photoperiodic flowering remain to be elucidated. In this study, we investigated how the diurnal expression pattern of the E1 gene is related to photoperiodic length; and to what extent allelic variation in the B3-like domain of the E1 gene is associated with flowering time phenotype. The bimodal expression of the E1 gene peaked first at around 2 hours after dawn in long-day condition. The basal expression level of E1 was enhanced by the long light phase, and decreased by duration of dark. We identified a 5bp (3 SNP and 2-bp deletion) mutation, referred to an e1-b3a, which occurs in the middle of B3 domain of the E1 gene in the early flowering cultivar Yanhuang 3. Subcellular localization analysis showed that the putative truncated e1-b3a protein was predominately distributed in nuclei, indicating the distribution pattern of e1-b3a was similar to that of E1, but not to that of e1-as. Furthermore, genetic analysis demonstrated allelic variations at the E1 locus significantly underlay flowering time in three F2 populations. Taken together, we can conclude the legume specific E1 gene confers some special features in photoperiodic control of flowering in soybean. Further characterization of the E1 gene will extend our understanding of the soybean flowering pathway in soybean.
Highlights
Soybean provides human beings with both good quality protein and oil
Basal expression level of the E1 gene is associated with the photoperiodic length
Some photoperiodic sensibility is still remaining in cultivars carrying the e1-nl null allele, reflecting some other pathways mediating photoperiodic sensibility still exist when the E1 gene is absent [26]
Summary
Soybean provides human beings with both good quality protein and oil. As early as the 1920s, researchers used soybean and other crop species as a model to study flowering time photoperiodic response, leading to the discovery and the advancement of photoperiodism [1–3]. The e2 allele caused early flowering possibly through modulation of expression of GmFT2a, one of the soybean florigen genes [15,19] Both E3 and E4 genes encode phytochrome A (PHYA) proteins. We identified a new E1 allele e1-b3a, a 5 bp compound variation in the middle of the B3-like domain, and further tested the effects of this allele on flowering time using an F2 population. The flowering time phenotypes between different Harosoy E1 near isogenic lines (NILs) were associated with the differential expression of the two GmFT-like genes both under SD and LD conditions, inferring that the E1 locus suppresses flowering through the modulation of GmFTs expression [24]. We identified a new allele with variation in the middle of the B3-like domain of the E1 gene, and further characterized the subcellular localization and functional effect of this allelic variation on flowering time in an F2 population. The function of the E1 gene and the interactions with other E genes were analyzed using F2 populations
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