| Soybean [Glycine max(L.) Merr.] is a major oil and protein crop globally. It is one of the most important commodities in the world. It can substantially provide oils, micronutrients, minerals, and vegetable proteins suitable for livestock feed and human consumption. In addition, soybean has supplied materials for industrial uses. Such diverse uses of soybean make it a more widely desired crop plant and are rapidly increasing its demand. However, drought is by far the most important environmental factor contributing to yield losses in crops, and it is a major constraint to the production and yield stability of soybean. Therefore, the study of the impact of drought on soybean and response mechanisms to drought in soybean, has important implications for selecting and breeding new varieties of drought tolerance. To evaluate the morphological traits and physiological characteristics of drought-resistant soybean mutant M18, PEG-6000 were applied at soybean germination stage, seedling stage and flowering stage as drought stress conditions. JN18, a wild-type line was selected as control. We also investigated agronomic traits of M18. In addition, we performed transcriptome sequencing of M18 in the seedling stage. The main results were as follows:1. The soybean drought-resistant mutant M18 with JN18 as the control were planted under both conditions of normal irrigation and drought stress. We evaluated the effects of drought stress on seed germination and seedling growth of soybean. The results showed that seed germination and seedling growth of soybean were significantly inhibited by drought stress in this experiment. With the strengthening of drought stress, seeds germination rate, germination index and vigor index were significantly reduced, taproot length, total length of lateral toots and plumule length of the seedlings were shortened, the number of lateral roots, root weight, lateral root weight and plumule weight were decreased. The results showed that M18 had higher seeds germination rate, germination index and vigor index under the same PEG treatment. M18 also showed a strong growth advantage under the same drought stress. Many indices of M18 were higher than JN18, including taproot length, number of lateral roots, plumule length. It was suggested that the ability of drought resistance of M18 was more superior than JN18.2. To evaluate the growth and physiological characteristics of drought-resistant soybean mutant M18, 0%, 5%, 15%, 25% of PEG-6000 were applied at soybean seedling stage as drought stress conditions. JN18, wild-type line was selected as control. The results showed that taproot length, number of lateral roots, total length of lateral roots, root volume, root dry weight of both M18 and JN18 increased initially and then decreased with the increasing of PEG concentration; the plant height, crown fresh weight, crown dry weight and RWC gradually decreased; the ratio of root/shoot, Procontent, MDA content, SOD activity and POD activity gradually increased. There was highly significant difference between dry root weight of M18 and J18. M18 had higher water retention, osmotic adjustment ability and enzymatic antioxidant capacity than those of J18 under the same drought stress. These morphological indexes and physiological characteristics including root volume, plant height, crown dry weight, and Pro content, could be used to evaluate drought resistance of soybean.3. Drought Resistance of M18 and JN18 in flowering stage indicated that M18 still showed strong drought resistance in the form of morphological indexes and physiological characteristics. The results showed that taproot length, number of lateral roots, the total length of lateral root, root volume and root dry weight increased with the growing degree of drought stress firstly and then decreased, and plant height, stem dry weight sessions and crown decreased, indicating that mild drought can promote root growth of soybean plants. Along with an increase in the degree of drought stress, the content of Pro, SS, MDA, and SOD activity were all gradually increased, only leaf RWC decreased, while POD activity, total chlorophyll content, chlorophyll a and chlorophyll b contents were firstly increased and then decreased. In the same treatment under drought stress, the total length of lateral roots, root volume and root dry weight of M18 were slightly higher than that of JN18, but it did not reach a significant difference; the SS content of M18 was significantly higher than that of JN18 at the same level of treatment; At 10%, 15% and 20% PEG treatment, Total chlorophyll content of M18 and chlorophyll a / chlorophyll b, were significantly higher than JN18; When concentration of PEG ≥15%, the leaves RWC and POD activity of M18 were all significantly higher than that of JN18, however, the MDA content was significantly lower than JN18. Osmotic adjustment ability and enzymatic antioxidant capacity of M18 were higher than JN18 at soybean flowering stage.4. Two consecutive years of field test results shows, the number of growing days of M18 is about 121 days, which is precocious than JN18 3 or 4 days. There is no significant difference between M18 and JN18 in the main agronomic traits. M18 has circular leaves, purple flowers, green stems, semi-upright growth habit, semideterminate growth habit, brown pods and seeds covered with brown tomentose, and its seed is black round particles with yellow coat. M18 seed kernel weight averaged 12.83 g, and it was significantly less than JN18. Test species found that M18 primarily increased production by increasing the effective number of branches, pods as well as grains per plant. Productivity measurement results showed that production of M18 was 3019 Kg/hm2, and the yield increased 8.10% compared with JN18.5. The drought-resistant soybean mutant M18 and wild type JN18 were used to analyze differentially expressed genes and explore the drought tolerance mechanism by RNA-Seq. In the present study, transcriptomes of roots at the stage of seeding were sequenced using Illumina/Solexa sequencing technology, respectively. In total, 9.35 Gb of sequence data and 46.31 M high quality reads were generated from M18 and JN18. For each of the samples, about 85 percent of reads were aligned on the reference genome. 835 new transcripts were found by high throughput sequencing since present databases may be incomplete. The sequences of new genes were compared to the database, 733 of them have annotation information. The differentially expressed genes were selected based on the expression profiles and RPKM method, we analysed differential expression genes between different samples. In summary, we restricted 572 genes that exhibited differential expression between JN18 and M18 groups, JN18 group as a control, of these, the expression levels of 227 genes were up-regulated in the M18 groups, the remaining 345 genes were down-regulated in the M18 groups. COG function classification of consensus sequence showed that the differentially expressed genes were primarily associated with general function prediction only, transcription, signal transduction mechanisms.6. The results of analyzing the GO functional annotations are presented that 13 terms corresponding to biological processes, 10 terms corresponding to molecular functions. In the biological processes category, the most important enriched terms are related to hormones metabolism and abiotic stress response. Pathway analysis showed that the differentially expressed genes were primarily associated with glycolysis/gluconeogenesis, cysteine and methionine metabolism, Plant hormone signal transduction. Among of them, 2 pathways were significantly enriched for differentially expressed genes. |
PDF Full Text Request