Global Journal of Science Frontier Research, G: Bio-Tech & Genetics, Volume 22 Issue 2

complex. Through this post-transcriptional regulation, auxin stabilizes the E2FA/B and DPA complex, which up- regulates the expression of genes essential for initiating the S phase (208), and thereby initiating the process of dormancy release. Hence, the growth inhibition in the dormant tuber meristem is a consequence of the arrest of tuber meristem cells at the G1 phase of the cell cycle. Cytokinin (CK) also play role in dormancy regulation at cellular level. It has been demonstrated that exogenous application of CK stimulates tuber dormancy breaking (115, 209), and endogenous CK can initiate the onset of dormancy release. Studies have revealed that exogenous application of zeatin upregulate CYCD3 in Arabidopsis and Camellia (115, 152), suggesting possible crosstalk between cytokinin, auxin and sucrose in activation of cyclin D genes during dormancy release. During the transition from dormancy to dormancy breaking phase of tuber, expression of genes encoding histone proteins (H3, H4, H2B) and other proteins such as MAP kinase, γ tubulin, and ovule/fibre elongation protein have been implicated in cell division and initiation of dormancy breaking (206). The implication of histone proteins (H3, H4, H2B) during cell division process is quite expected, because these histone proteins are the DNA packing materials and during synthesis or replication, the DNAs are unpacked thereby releasing the packing materials (histone proteins). Furthermore, histones also function as receptors of environmental signals (temperature and light) which act through phytochromes signaling (PIFs) to induce gibberellins (GAs) biosynthesis (Fig4), which in turn initiate dormancy release and germination process. IV. C onclusions and F uture P erspectives Dormancy and sprouting are important stages of tuber development providing for successive vegetative growth and regeneration of yam tubers. Characteristics of tuber dormancy, its duration in particular, are stable hereditary traits. Tuber dormancy and sprouting include a complex of different, but coupled physiological and biochemical processes. The main ones are growth and its active blocking, as well as storage and active usage of sugars and proteins. Though, how these processes are integrated at the molecular, physiological and genetic levels and how they are coordinated with each other in regulation of dormancy induction and germination have been extensively studied using modern tools in other crops including potato tuber and the processes are highly conserved across crop species, but in yam crop such studies are still lacking. Such studies are particularly important in yam crop, in view of long dormancy duration phenotype of its tuber, which has constituted a major constraint in yam research and genetic improvement and consequently imped unlocking of its productive and utilization potentials. It has been established through elegant studies that the process of dormancy induction and breaking is a complex, separate, but continuous physiological and molecular processes involving wide range of hormones, sugars, cellular activities and their regulatory networks crosstalk, leading to expression of many genes that function in a coordinated manner to determine crop phenotype with regards to dormancy duration and germination. It was demonstrated that Abscisic acid (ABA), Gibberellins (GAs), Auxins, sugar signaling pathways and their regulatory networks crosstalk are the key master players in regulation of crop dormancy and germination. Particularly, it has been shown that sugars, non- fermenting related kinase 1 ( SnRK1 ) and to lesser extent basic leucine zipper (b/ZIP) group of protein motifs play prominent roles in all the major dormancy induction and maintenance regulatory pathways, for example, in ABA, GA, Auxins, Low sugar signals and cell cycle active blocking at G1 phase, SnRK1 and b/ZIP are involved and their actions are also conserved across plant species so far studied. Therefore, focusing on their roles in search of solution to long duration dormancy phenotype of yam tuber, might provide veritable opportunity for tuber dormancy to be manipulated to fit the agronomically desired tuber dormancy phenotype, through genetic engineering of any of the regulatory networks without yield and food quality trade off. Declarations Ethical Approval Not applicable Competing Interest The authors have declared that there’s no competing interest associated with this article, in any financial, patent ownership and personal relationships Funding This work was supported with funding from GENES Intra-Africa Academic Mobility Project; “Mobility for plant genomics scholars to accelerate climate-smart adaptation options and food security in Africa (GENES)” funded by European Union. Availability of data and materials Not applicable R eferences R éférences R eferencias 1. Dansi A, Dantsey-Barry H, Dossou-Aminon I, N’Kpenu EK, Agré AP, Sunu YD, et al. Varietal diversity and genetic erosion of cultivated yams (Dioscorea cayenensis Poir - D. rotundata Lam complex and D. alata L.) in Togo. Int J Biodivers Conserv 1998;5: 223–39. 2. Gamiette F, Bakry F., G. A. Ploidy determination of some yam species (Dioscorea spp.) by flow cytometry and conventional chromosomes counting. Genet Resour Crop Evol 1999;46:19-27. 1 Year 2022 67 © 2022 Global Journals Global Journal of Science Frontier Research Volume XXII Issue ersion I VII ( G ) Physiological and Molecular basis of Dormancy in Yam Tuber: A Way Forward towards Genetic Manipulation of Dormancy in Yam Tubers