Browsing by Author "Sun, Li (TTU)"
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Item The B’ζ subunit of protein phosphatase 2A negatively regulates ethylene signaling in Arabidopsis(2021) Zhu, Xunlu (TTU); Shen, Guoxin; Wijewardene, Inosha (TTU); Cai, Yifan (TTU); Esmaeili, Nardana (TTU); Sun, Li (TTU); Zhang, Hong (TTU)Ethylene is a major plant hormone that regulates plant growth, development, and defense responses to biotic and abiotic stresses. The major pieces of the ethylene signaling pathway have been put together, although several details still need to be elucidated. For instance, the phosphorylation and dephosphorylation processes controlling the ethylene responses are poorly understood and need to be further explored. The type 2A protein phosphatase (PP2A) was suggested to play an important role in the regulation of ethylene biosynthesis, where the A1 subunit of PP2A was shown to be involved in the regulation of the rate-limiting enzyme of the ethylene biosynthetic pathway. However, whether other subunits of PP2A play roles in the ethylene signal transduction pathway is yet to be answered. In this study, we demonstrate that a B subunit, PP2A-B’ζ, positively regulates plant germination and seedling development, as a pp2a-b’ζ mutant is very sensitive to ethylene treatment. Furthermore, PP2A-B’ζ interacts with and stabilizes the kinase CTR1 (Constitutive Triple Response 1), a key enzyme in the ethylene signal transduction pathway, and like CTR1, PP2A-B’ζ negatively regulates ethylene signaling in plants.Item Co-overexpressing a Plasma Membrane and a Vacuolar Membrane Sodium/Proton Antiporter Significantly Improves Salt Tolerance in Transgenic Arabidopsis Plants(2016) Pehlivan, Necla; Sun, Li (TTU); Jarrett, Philip (TTU); Yang, Xiaojie; Mishra, Neelam (TTU); Chen, Lin; Kadioglu, Asim; Shen, Guoxin; Zhang, Hong (TTU)The Arabidopsis gene AtNHX1 encodes a vacuolar membrane-bound sodium/proton (Na+/H+) antiporter that transports Na+ into the vacuole and exports H+ into the cytoplasm. The Arabidopsis gene SOS1 encodes a plasma membrane-bound Na+/H+ antiporter that exports Na+ to the extracellular space and imports H+ into the plant cell. Plants rely on these enzymes either to keep Na+ out of the cell or to sequester Na+ into vacuoles to avoid the toxic level of Na+ in the cytoplasm. Overexpression of AtNHX1 or SOS1 could improve salt tolerance in transgenic plants, but the improved salt tolerance is limited. NaCl at concentration >200 mM would kill AtNHX1-overexpressing or SOS1-overexpressing plants. Here it is shown that co-overexpressing AtNHX1 and SOS1 could further improve salt tolerance in transgenic Arabidopsis plants, making transgenic Arabidopsis able to tolerate up to 250 mM NaCl treatment. Furthermore, co-overexpression of AtNHX1 and SOS1 could significantly reduce yield loss caused by the combined stresses of heat and salt, confirming the hypothesis that stacked overexpression of two genes could substantially improve tolerance against multiple stresses. This research serves as a proof of concept for improving salt tolerance in other plants including crops.Item Co-overexpression of AVP1 and PP2A-C5 in Arabidopsis makes plants tolerant to multiple abiotic stresses(2018) Sun, Li (TTU); Pehlivan, Necla; Esmaeili, Nardana (TTU); Jiang, Weijia; Yang, Xiaojie; Jarrett, Philip (TTU); Mishra, Neelam (TTU); Zhu, Xunlu (TTU); Cai, Yifan (TTU); Herath, Maheshika (TTU); Shen, Guoxin; Zhang, Hong (TTU)Abiotic stresses are major threats to agricultural production. Drought and salinity as two of the major abiotic stresses cause billions of losses in agricultural productivity worldwide each year. Thus, it is imperative to make crops more tolerant. Overexpression of AVP1 or PP2A-C5 was previously shown to increase drought and salt stress tolerance, respectively, in transgenic plants. In this study, the hypothesis that co-overexpression of AVP1 and PP2A-C5 would combine their respective benefits and further improve salt tolerance was tested. The two genes were inserted into the same T-DNA region of the binary vector and then introduced into the Arabidopsis genome through Agrobacterium-mediated transformation. Transgenic Arabidopsis plants expressing both AVP1 and PP2A-C5 at relatively high levels were identified and analyzed. These plants displayed enhanced tolerance to NaCl compared to either AVP1 or PP2A-C5 overexpressing plants. They also showed tolerance to other stresses such as KNO3 and LiCl at harmful concentrations, drought, and phosphorus deficiency at comparable levels with either AVP1 or PP2A-C5 overexpressing plants. This study demonstrates that introducing multiple genes in single T-DNA region is an effective approach to create transgenic plants with enhanced tolerance to multiple stresses.Item Comparative proteomic analysis of Gossypium thurberi in response to Verticillium dahliae inoculation(2015) Fang, Weiping; Xie, Deyi; Zhu, Heqin; Li, Wu; Xu, Zhenzhen; Yang, Lirong; Li, Zhifang; Sun, Li (TTU); Wang, Jinxia; Nie, Lihong; Tang, Zhongjie; Lv, Shuping; Zhao, Fu’An; Sun, Yao; Zhao, Yuanming; Hou, Jianan; Yang, XiaojieVerticillium wilt is threatening cotton productivity globally. This disease is caused by soil-borne Verticillium dahliae which directly infects cotton roots, and exclusively colonizes and occludes xylem vessels, finally resulting in necrosis, defoliation, and most severely, plant death. For the first time, iTRAQ (isobaric tags for relative and absolute quantification) was applied to screen the differentially expressed proteins of OPEN ACCESS Gossypium thurberi inoculated with V. dahliae. A total of 6533 proteins were identified from the roots of G. thurberi after inoculation with V. dahliae, and 396 showed up- and 279 down-regulated in comparison to a mock-inoculated roots. Of these identified proteins, the main functional groups were those involved in cell wall organization and reinforcement, disease-resistant chemicals of secondary metabolism, phytohormone signaling, pathogenesis-related proteins, and disease-resistant proteins. Physiological and biochemical analysis showed that peroxidase activity, which promotes the biosynthesis and accumulation of lignin, was induced early in the hypocotyl after inoculation with V. dahliae. Similarly, salicylic acid also accumulated significantly in hypocotyl of the seedlings after inoculation. These findings provide an important knowledge of the molecular events and regulatory networks occurring during G. thurberi-V. dahliae interaction, which may provide a foundation for breeding disease-resistance in cotton.Item The Effects of Transcription Directions of Transgenes and the gypsy Insulators on the Transcript Levels of Transgenes in Transgenic Arabidopsis(2017) Jiang, Weijia; Sun, Li (TTU); Yang, Xiaojie; Wang, Maohua; Esmaeili, Nardana (TTU); Pehlivan, Necla; Zhao, Rongli; Zhang, Hong (TTU); Zhao, YunManipulation of a single abiotic stress-related gene could improve plant performance under abiotic stress conditions. To simultaneously increase plant tolerance to multiple stresses, it is usually required to overexpress two (or more) genes in transgenic plants. The common strategy is to assemble two or more expression cassettes, where each gene has its own promoter and terminator, within the same T-DNA. Does the arrangement of the two expression cassettes affect expression of the two transgenes? Can we use the Drosophila gypsy insulator sequence to increase the expression of the two transgenes? Answers to these questions would contribute to design better transformation vectors to maximize the effects of multi-gene transformation. Two Arabidopsis genes, PP2A-C5 and AVP1, and the gypsy insulator sequence were used to construct six transformation vectors with or without the gypsy insulator bracketing the two expression cassettes: uni-directional transcription, divergent transcription, and convergent transcription. Total RNAs were isolated for reverse transcription- quantitative real-time polymerase chain reaction (RT-qPCR) assays and a thorough statistical analysis was conducted for the RT-qPCR data. The results showed that the gypsy insulator does promote the expression of two transgenes in transgenic plants. Besides, the plants containing the divergent transcription cassettes tend to have more correlated expression of both genes.Item Identification and Functional Analysis of microRNAs Involved in the Anther Development in Cotton Genic Male Sterile Line Yu98-8A(2016) Yang, Xiaojie; Zhao, Yuanming; Xie, Deyi; Sun, Yao; Zhu, Xunlu (TTU); Esmaeili, Nardana (TTU); Yang, Zuoren; Wang, Ye; Yin, Guo; Lv, Shuping; Nie, Lihong; Tang, Zhongjie; Zhao, Fu'an; Li, Wu; Mishra, Neelam (TTU); Sun, Li (TTU); Zhu, Wei; Fang, WeipingHybrid vigor contributes in a large way to the yield and quality of cotton (Gossypium hirsutum) fiber. Although microRNAs play essential regulatory roles in flower induction and development, it is still unclear if microRNAs are involved in male sterility, as the regulatory molecular mechanisms of male sterility in cotton need to be better defined. In this study, two independent small RNA libraries were constructed and sequenced from the young buds collected from the sporogenous cell formation to the meiosis stage of the male sterile line Yu98-8A and the near-isogenic line. Sequencing revealed 1588 and 1536 known microRNAs and 347 and 351 novel miRNAs from male sterile and male fertile libraries, respectively. MicroRNA expression profiles revealed that 49 conserved and 51 novel miRNAs were differentially expressed. Bioinformatic and degradome analysis indicated the regulatory complexity of microRNAs during flower induction and development. Further RT-qPCR and physiological analysis indicated that, among the different Kyoto Encyclopedia Gene and Genomes pathways, indole-3-acetic acid and gibberellic acid signaling transduction pathways may play pivotal regulatory functions in male sterility.Item Morphological, Physiological and Proteomic Analyses Provide Insights into the Improvement of Castor Bean Productivity of a Dwarf Variety in Comparing with a High-Stalk Variety(2016) Hu, Wenjun; Chen, Lin; Qiu, Xiaoyun; Lu, Hongling; Wei, Jia; Bai, Yueqing; He, Ningjia; Hu, Rongbin (TTU); Sun, Li (TTU); Zhang, Hong (TTU); Shen, GuoxinRicinus communis displays a broad range of phenotypic diversity in size, with dwarf, common, and large-sized varieties. To better understand the differences in plant productivity between a high-stalk variety and a dwarf variety under normal growth conditions, we carried out a comparative proteomic study between Zhebi 100 (a high stalk variety) and Zhebi 26 (a dwarf variety) combined with agronomic and physiological analyses. Over 1000 proteins were detected, 38 of which differed significantly between the two varieties and were identified by mass spectrometry. Compared with Zhebi 100, we found that photosynthesis, energy, and protein biosynthesis related proteins decreased in abundance in Zhebi 26. The lower yield of the dwarf castor is likely related to its lower photosynthetic rate, therefore we hypothesize that the lower yield of the dwarf castor, in comparing to high stalk castor, could be increased by increasing planting density. Consequently, we demonstrated that at the higher planting density in Zhebi 26 (36,000 seedlings/hm2) can achieve a higher yield than that of Zhebi 100 (12,000 seedlings/hm2). Proteomic and physiological studies showed that for developing dwarf R. communis cultivar that is suitable for large scale-production (i.e., mechanical harvesting), it is imperative to identify the optimum planting density that will contribute to higher leaf area index, higher photosynthesis, and eventually higher productivity.Item Students’ Motivation and Affection Profiles and Their Relation to Mathematics Achievement, Persistence, and Behaviors(2021) Xiao, Feiya; Sun, Li (TTU)Objective: We aimed to explore profiles of subgroups of United States students based on their motivational and affective characteristics and investigate the differences in math-related behaviors, persistence, and math achievement across profiles. Method: We used 1,464 United States students (male 743 51%, female 721 49%, age 15.82 ± 0.28) from PISA 2012 United States data in our study. First, we employed latent profile analysis and secondary clustering to identify subgroups of students based on motivational (math self-concept, interest in math, perceived control, and instrumental motivation) and affective factors (math anxiety). Next, we used regression to compare differences in math behavior, persistence, and achievement among all identified subgroups. Results: We found five distinct groups of students with different patterns of motivation and affection. The subgroup of students with the lowest math anxiety and the highest motivation levels showed the highest math achievement and levels of persistence. The groups with high math interest, math self-concept, and instrumental motivation showed the most frequent math-related behaviors. Conclusions: Our findings reveal the complexity of the students’ motivational and affective profiles. Our findings are significant for teachers and educators to understand the diversity of students and provide theoretical and practical support for individualized and differentiated instruction.Item The yield difference between wild-type cotton and transgenic cotton that expresses IPT depends on when water-deficit stress is applied(2018) Zhu, Xunlu (TTU); Sun, Li (TTU); Kuppu, Sundaram (TTU); Hu, Rongbin (TTU); Mishra, Neelam (TTU); Smith, Jennifer (TTU); Esmaeili, Nardana (TTU); Herath, Maheshika (TTU); Gore, Michael A.; Payton, Paxton; Shen, Guoxin; Zhang, Hong (TTU)Drought is the No. 1 factor that limits agricultural production in the world, thus, making crops more drought tolerant is a major goal in agriculture. Many genes with functions in abiotic stress tolerance were identified, and overexpression of these genes confers increased drought tolerance in transgenic plants. The isopentenyltransferase gene (IPT) that encodes a rate limiting enzyme in cytokinin biosynthesis is one of them. Interestingly, when IPT-transgenic cotton was field-tested at two different sites, Texas and Arizona, different results were obtained. To explain this phenomenon, reduced irrigation experiments with different timing in applying water deficit stress were conducted. It was found that the timing of water deficit stress is critical for IPT-transgenic cotton to display its yield advantage over control plants (i.e. wild-type and segregated non-transgenic plants). If water deficit stress occurs before flowering (vegetative phase), IPT-transgenic cotton would outperform control plants; however, if water deficit stress occurs at or after flowering (reproductive phase), there would not be a yield difference between IPT-transgenic and control cotton plants. This result suggests that an early induction of IPT expression (before first flowering) is needed in order to realize the benefits of IPT-expression in transgenic plants that face water-deficit stress later in development.Item Transcriptomic Profiling Reveals Complex Molecular Regulation in Cotton Genic Male Sterile Mutant Yu98-8A(2015) Fang, Weiping; Zhao, Fu'an; Sun, Yao; Xie, Deyi; Sun, Li (TTU); Xu, Zhenzhen; Zhu, Wei; Yang, Lirong; Zhao, Yuanming; Lv, Shuping; Tang, Zhongjie; Nie, Lihong; Li, Wu; Hou, Jianan; Duan, Zhengzheng; Yu, Yuebo; Yang, XiaojieAlthough cotton genic male sterility (GMS) plays an important role in the utilization of hybrid vigor, its precise molecular mechanism remains unclear. To characterize the molecular events of pollen abortion, transcriptome analysis, combined with histological observations, was conducted in the cotton GMS line, Yu98-8A. A total of 2,412 genes were identified as significant differentially expressed genes (DEGs) before and during the critical pollen abortion stages. Bioinformatics and biochemical analysis showed that the DEGs mainly associated with sugars and starch metabolism, oxidative phosphorylation, and plant endogenous hormones play a critical and complicated role in pollen abortion. These findings extend a better understanding of the molecular events involved in the regulation of pollen abortion in genic male sterile cotton, which may provide a foundation for further research studies on cotton heterosis breeding.Item Water-Deficit Inducible Expression of a Cytokinin Biosynthetic Gene IPT Improves Drought Tolerance in Cotton(2013) Kuppu, Sundaram (TTU); Mishra, Neelam (TTU); Hu, Rongbin (TTU); Sun, Li (TTU); Zhu, Xunlu (TTU); Shen, Guoxin; Blumwald, Eduardo; Payton, Paxton; Zhang, Hong (TTU)Water-deficit stress is a major environmental factor that limits agricultural productivity worldwide. Recent episodes of extreme drought have severely affected cotton production in the Southwestern USA. There is a pressing need to develop cotton varieties with improved tolerance to water-deficit stress for sustainable production in water-limited regions. One approach to engineer drought tolerance is by delaying drought-induced senescence via up-regulation of cytokinin biosynthesis. The isopentenyltransferase gene (IPT) that encodes a rate limiting enzyme in cytokinin biosynthesis, under the control of a water-deficit responsive and maturation specific promoter PSARK was introduced into cotton and the performance of the PSARK::IPT transgenic cotton plants was analyzed in the greenhouse and growth chamber conditions. The data indicate that PSARK::IPT-transgenic cotton plants displayed delayed senescence under water deficit conditions in the greenhouse. These plants produced more root and shoot biomass, dropped fewer flowers, maintained higher chlorophyll content, and higher photosynthetic rates under reduced irrigation conditions in comparison to wild-type and segregated non-transgenic lines. Furthermore, PSARK::IPT-transgenic cotton plants grown in growth chamber condition also displayed greater drought tolerance. These results indicate that water-deficit induced expression of an isopentenyltransferase gene in cotton could significantly improve drought tolerance.