| Drought stress(DS) serious ly limits the growth and development of tea plants, thus affect ing crop yield and quality. To effectively cope with DS, breeding the drought-resistant tea plant is one of the most important biological measures. A comprehensive understanding of the response of plants to DS at morphological, physiological and molecular levels would be benef icial for breeding the drought-resistant tea plants. In the present study, responses to soil drying and rewatering were measured at morphological and physiological levels in two tea cultivars including drought-susceptible ?Zhuyeqi‘(T1) and drought-tolerant ?Ningzhou 2‘(T2) grown under indoor and outdoor conditions. To deeper elucidate the molecular mechanisms regarding tea plants response to dehydration and rehydration, based on morphological and physiological changes, before DS as well as during DS and recovery, samples of ?two and a bud‘ from T2 were used for RNA-sequencing(RNA-Seq). Additionally, the key enzyme genes for abscisic acid(ABA) synthesis and signal transduction in tea plant were cloned. The main results of this dissertation are as follow:1. Under DS and recovery, the ABA and salicylic acid(SA) content peaked in the early stage of DS and then decreased rapidly in two tea cultivars. In contrast, the malondialdehyde(MDA), soluble sugars(SS) and proline(Pro) contents as well as superoxide dismutase(SOD) and catalase(CAT) activities in two cultivars increased significantly as DS progressed and then rapidly decreased following rehydration. T2 had a lower concentration of MDA, SS and Pro than T1 throughout dehydration and rehydration, and was characterized by lower ABA and higher SA accumulation. Furthermore, T2 had higher effective SOD –CAT antioxidative defense systems and recovery capability in comparison to T12. We carried out large-scale RNA-Seq of tea plants before DS as well as during and after DS using the Illumina Hi Seq? 2000 platform. A total of ~21.8 million high-quality trimmed reads were produced and then assembled into 60,587 unigenes with an average length of 706 bp. Based on similarity search with known proteins in public protein databases, 48,089 unigenes(79.4%) were functionally annotated. These unigenes mainly involved in metabolic pathways and hormone signal transduction under DS, while anabolism under recovery. In total, 5,955 differentially expressed genes(DEGs)were identif ied before drought as well as during DS and recovery. Among these genes, 1,517 DEGs were down-regulated first and then up-regulated during the three stages, while 490 down-regulated DEGs and 156 up-regulated DEGs were screened out, but 3,792 DEGs were up-regulated first and then down-regulated. The q RT-PCR analys is of 20 randomly-selected genes showed close concordance with RNA-Seq3. A total of 547 and 604 transcription factor genes belonging to 58 families were identified under DS and RC, respectively. In total, 762 and 950 protein kinase genes belonging to 58 families were observed during and after DS, respectively. In addition, total 53 and 81 protein phosphatase genes were observed under dehydration and rehydration respectively and classified into two families. Mechanisms of hormone metabolism and signal transduction as well as soluble sugar and proline metabolism in tea plant were elucidated. These rsponses had crucial roles in tea plants resistance to DS. Under DS and recovery, the expression level of NCED1, PAL, SOD and CAT was significantly positively correlated with ABA and S A content as well as SOD and CAT activity in two cultivars, respectively. A signif icant positive correlation between the P5 CS expression level and the Pro content was observed in T2, while P5 CS expression level was subjected to feedback inhibition by Pro in T1. In general, T2 showed more drastic changes in the expression of five selected genes during and after DS.4. NCED1 and NCED4 as well as Sn RK2.1―Sn RK2.4 as the key enzymes genes for ABA synthesis and signal transduction respectively were cloned. Their functions in drought resistance were preliminarily validated by measuring their expression patterns during and after DS using q RT-PCR. In addition, ABA regulation of stomatal movement in tea plants was preliminarily clar ified under DS and recovery. |
