Abstract
Dioecy (distinct male and female individuals) and scarce to non-flowering are common features of cultivated yam (Dioscorea spp.). However, the molecular mechanisms underlying flowering and sex determination in Dioscorea are largely unknown. We conducted SuperSAGE transcriptome profiling of male, female and monoecious individuals to identify flowering and sex-related genes in white Guinea yam (D. rotundata), generating 20,236 unique tags. Of these, 13,901 were represented by a minimum of 10 tags. A total 88 tags were significantly differentially expressed in male, female and monoecious plants, of which 18 corresponded to genes previously implicated in flower development and sex determination in multiple plant species. We validated the SuperSAGE data with quantitative real-time PCR (qRT-PCR)-based analysis of the expression of three candidate genes.We further investigated the flowering patterns of 1938 D. rotundata accessions representing diverse geographical origins over two consecutive years. Over 85% of accessions were either male or non-flowering, less than 15% were female, while monoecious plants were rare. Intensity of flowering varied between male and female plants, with the former flowering more abundantly than the latter. Candidate genes identified in this study can be targeted for further validation and to induce regular flowering in poor to non-flowering cultivars. Findings of the study provide important inputs for further studies aiming to overcome the challenge of flowering in yams and to improve efficiency of yam breeding.
Highlights
White Guinea yam, Dioscorea rotundata Poir., is the most preferred and widely cultivated yam species in West-Africa [1]
The flowering patterns of 1938 D. rotundata accessions collected primarily from the main yam growing regions of West and Central Africa were assessed under field conditions at IITA over two consecutive growing seasons in 2010 and 2011
D. rotundata accessions are distinguished based on morphology of their flowers as female, male, or monoecious (Fig 1)
Summary
White Guinea yam, Dioscorea rotundata Poir., is the most preferred and widely cultivated yam species in West-Africa [1]. Despite its considerable economic and socio-cultural importance, genetic improvement of cultivated yam remains difficult and slow due to its dioecy and poor to non-flowering nature [2]. The presence of distinct male and female individuals, is one of the major characteristics of the genus Dioscorea [3]. A major breeding challenge associated with dioecy is that synchronizing flowering time is difficult when making genetic crosses. A more recent study has revealed that sex determination in the cultivated African species of D. rotundata follows the ZZ (male) and ZW (female) system [9]. A candidate chromosomal region associated with sex was determined and a diagnostic marker for sex determination developed. Gene(s) functionally responsible for sex determination are yet to be identified in yam species
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