Browsing by Author "Zhu, Xunlu (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-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 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 Steroidal antibiotics are antimetabolites of Acanthamoeba steroidogenesis with phylogenetic implications(2019) Zhou, Wenxu (TTU); Ramos, Emilio (TTU); Zhu, Xunlu (TTU); Fisher, Paxtyn M. (TTU); Kidane, Medhanie E. (TTU); Vanderloop, Boden H. (TTU); Thomas, Crista D. (TTU); Yan, Juqiang (TTU); Singha, Ujjal; Chaudhuri, Minu; Nagel, Michael T. (TTU); David Nes, W. (TTU)Pathogenic organisms may be sensitive to inhibitors of sterol biosynthesis, which carry antimetabolite properties, through manipulation of the key enzyme, sterol methyltransferase (SMT). Here, we isolated natural suicide substrates of the ergosterol biosynthesis pathway, cholesta-5,7,22,24-tetraenol (CHT) and ergosta-5,7,22,24(28)-tetraenol (ERGT), and demonstrated their interference in Acanthamoeba castellanii steroidogenesis: CHT and ERGT inhibit trophozoite growth (EC50 of 51 nM) without affecting cultured human cell growth. Washout experiments confirmed that the target for vulnerability was SMT. Chemical, kinetic, and protein-binding studies of inhibitors assayed with 24-AcSMT [catalyzing C28-sterol via 24(28)-olefin production] and 28-AcSMT [catalyzing C29-sterol via 25(27)-olefin production] revealed interrupted partitioning and irreversible complex formation from the conjugated double bond system in the side chain of either analog, particularly with 28-AcSMT. Replacement of active site Tyr62 with Phe or Leu residues involved in cation- interactions that model product specificity prevented protein inactivation. The alkylating properties and high selective index of 103 for CHT and ERGT against 28-AcSMT are indicative of a new class of steroidal antibiotic that, as an antimetabolite, can limit sterol expansion across phylogeny and provide a novel scaffold in the design of amoebicidal drugs. Animal studies of these suicide substrates can further explore the potential of their antibiotic properties.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 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.