The Molecular Mechanism Of Vernalization Induced By Low Temperature In Oriental Hybrid Lily ’Sorbonne’

Lily bulb has the characteristics of natural dormancy, can only germinate, grow, blossom under the right condition generally after the dormancy. This study was about physiological changes and molecular changes of lily in the vernalization process from morphology, physiology, transcriptomics and proteomics through research and bioinformatics analysis.The main results are described as follows:1 In physiological mechanism, the distance between the bud growing point to the top of bulb of ’Sorbonne’ was less than 1 cm stored at 4℃ for 49 days, basically as same as the morphological mark, indicating that lily bulbs had broke dormancy at this time. Concentrations of soluble sugars also changed during bulb cold storage, which increased as the chilling term increased to 49 days but decreased afterward. Concentration of endogenous abscisic acid (ABA) level in the bulbs decreased as storage duration increased, and it remained at a constant level after being stored for 35 days. ABA and IAA levels changed significantly, indicating that ABA and IAA played important roles in dormancy-breaking process. GA plays an important role in the formation of flower buds. In addition, the role of each hormone is not alone but by interacting with each other to control bulbs dormancy and only when in a state of equilibrium between the content of several hormones, it can cause the starting or maintaining the state of growth2 During the vernalization of Oriental hybrid lily’Sorbonne’, a large part of genes associated with plant development are belonging to MADS-box genes. Our study found a total of 378 unigenes encoding transcription factors, of which 64 belong to MIKC type MADS-box genes,314 belong to the M-type MADS-box genes. Our study found that 26 MIKC type unigenes expressed differentially during lily vernalization process, the majority were homologous to floral organ development-related genes, proving that the procedure of lily flower organs had already started in the early vernalization of lily. In addition to these transcription factors, our study also showed that ARF and MYB transcription factors were also significantly unregulated during lily vernalization at low temperature. These types of transcription factor family directly or indirectly regulated genes through regulation of flowering pathway, thereby affecting floral development, proving that auxin played an important role in lily flowering during vernalization. These genes of transcription factors are important candidate gene resources to improve lily flowering. Through the transcriptome data mining, we found lily histone modifications were associated with genes:genes histone deacetylase HDAC and DNA methyltransferase gene CMT. Vernalization could promote the increase of these two genes, and with the extension of vernalization time, the expression levels kept rising indicating that these two genes played a role mainly in the shoot apex, may be associated with the promotion of the process of vernalization gene expression.3 During the vernalization of Oriental hybrid lily’Sorbonne’, proteins related to amino acid metabolism accounted for 35% of all differential protein spots, proteins related to starch and sugar metabolism accounted for 22% of all differential protein spots, proteins related to hormone signal transduction accounted for 18% of all differential protein spots, proteins related to signal transduction accounted for 6% of all differential protein spots, proteins related to transport accounted for 22% of all differential protein spots. The function of these differentially expressed proteins mainly divided into metabolism, protein fate, cell defense, cell synthesis, binding protein components and auxiliary factors. These differentially expressed proteins played an important role in cell morphogenesis, carbohydrate metabolism, amino acid metabolism, synthesis of oxidative senescence and ethylene signaling. After analysis, carbohydrate synthesis pathway, and hormone regulation pathway may be an important endogenous regulators in regulating lily vernalization. In short, these differentially expressed proteins were involved in multiple physiological processes, they may work together to lead lily to pass vernalization induced by low temperature, and then squaring blossom.4 In addition, we identified two vernalizaiton-related genes (LoSVP and LoVRN1) from the cDNA library, which appear to be promising candidates for playing key roles in the development and response of flowering in Oriental lily plants. Through the Arabidopsis transgenic technology, we found that LoSVP had a role in inhibiting vernalization in response to low temperature, and could delay lily blossom time. But on the contrary, LoVRNl gene had a role in promoting vernalization in response to low temperature, and could promote the early blossom, and it was certain that LoVRNl had an effect on the change of the lily flower type.