The Plant Biotechnology Post-doctoral Oral Presentation Competition was held on Monday June 13th. The judges were Dr. Dennis Gray from the University of Florida, Dr. Prakash Kumar from the National University of Singapore and Dr. Nirmal Joshee from the Fort Valley State University. Dr. Bin Tian received the first prize for his talk “Host-derived Gene Silencing of Pathogen Fitness Genes Improves Resistance to Soybean Cyst Nematodes in Soybean” followed by Dr. Anne-Catherine Vanhove (second prize) for her talk “Evaluating Survival in Shoot Tips of Several Species Stored in Liquid Nitrogen for 4 to 16 Years”. Dr. Ratna Karan who talked about his research on “Improving Photosynthetic Efficiency in Sugarcane by Expression of Pyruvate Orthophosphate Dikinase from Miscanthus x giganteus” received the third prize.
Submitted by Sadanand Dhekney
Host-derived Gene Silencing of Pathogen Fitness Genes Improves Resistance to Soybean Cyst Nematodes in Soybean
Soybean cyst nematode (SCN), Heterodera glycines, is one of the most important pests to limit soybean production worldwide. Losses are estimated at 1 billion US dollars annually for the United States alone. RNA interference (RNAi) has become a powerful tool that can be used to silence many genes of interest. We report here that the expression of hairpin RNAi sequences derived from two SCN genes related to reproduction and fitness, HgY25 and HgPrp17, enhances resistance of soybean plants to SCN. Our previous studies using transgenic hairy root assays showed that transgenic composite plants expressing hairpin RNAi constructs targeting several SCN genes improved resistance against the nematodes. In current studies, bioassays performed on stable transgenic lines targeting SCN HgY25 and HgPrp17 fitness genes showed consistently significant reductions of 54% and 56% for eggs/g root, respectively. The analyses of T2 to T4 generations of transgenic soybeans by molecular detection and next generation sequencing confirmed the presence of specific short interfering RNAs complementary to target SCN genes. Targeted mRNAs of SCN eggs collected from the transgenic soybean lines were shown to be efficiently downregulated as confirmed by real time quantitative PCR. Based on the small RNA-seq data and bioassays, it is our hypothesis that a threshold of small interfering RNA molecules is required to significantly reduce SCN populations feeding on the host. Our results demonstrate that host-induced gene silencing of essential SCN fitness genes can be an effective strategy for enhancing resistance in crop plants.
Bin Tian, Kansas State University, Department of Plant Pathology, 1712 Claflin Road, Manhattan, KS 66506. In Vitro Cellular and Developmental Biology, 52:S33, 2016
Evaluating Survival in Shoot Tips of Several Species Stored in Liquid Nitrogen for 4 to 16 Years
Cryopreservation has been utilized for several decades, but little is known about the long-term survival of the stored plant material especially when it is used as a tool in the ex situ conservation of threatened and endangered species. The CryoBioBank® at CREW offers the opportunity to study the effects of long-term storage on cryopreserved samples. For this study, shoot tip samples of several species are being removed from the liquid nitrogen storage tanks and assessed for viability after 4-16 years in cryostorage. Shoot tip samples were removed from liquid nitrogen, thawed, placed on recovery medium, and evaluated for recovery at 4 weeks, using the same procedures as used at the time of banking. A preliminary analysis of data from four endangered, U.S. species (Crotalaria avonensis, Deeringothamnus rugelii, D. pulchellus and Hedeoma todsenii) shows at least some survival in 62% of all the samples. Of the tested variables, neither time in storage nor cryopreservation procedure explain any significant variation in the survival of the shoot tips, but species does explain significant variation. This suggests that the unique physiology of the species, rather than the length of storage, may be the most important factor in determining the survival of plant shoot tips following cryostorage. This highlights the importance of species-specific optimizations over broad generalizations in recommended storage techniques. These preliminary results show that long-term storage of shoot tips in liquid nitrogen is a viable tool in ex situ conservation. (This work supported in part by Institute of Museum and Library Services grant # LG-25-12-0595).
Anne-Catherine Vanhove, Center for Conservation and Research of Endangered Wildlife (CREW), Cincinnati Zoo and Botanical Garden, 3400 Vine Street, Cincinnati, OH, 45220. In Vitro Cellular and Developmental Biology, 52:S33-34, 2016
Improving Photosynthetic Efficiency in Sugarcane by Expression of Pyruvate Orthophosphate Dikinase from Miscanthus x giganteus.
Sugarcane is a highly productive C4 crop used as main source for table sugar and an important feedstock for bioethanol production. Improving photosynthetic efficiency in sugarcane will further boost its economic value. Pyruvate orthophosphate dikinase (PPDK) regenerates the substrate phosphoenol pyruvate (PEP) for the initial carbon-fixation step and has been proposed as rate limiting enzyme in C4 photosynthesis. A recent study also suggests that Miscanthus x giganteus (Mxg) achieves cold tolerance by increasing the amount of PPDK rather than its intrinsic properties. We evaluated MxgPPDK expression for improvement of photosynthesis and biomass accumulation in transgenic sugarcane grown under replicated field conditions. Pre-cultured cross-sections of immature sugarcane leaf whorls were used as target for biolistic transfer of MxgPPDK4 genomic clone under its native regulatory sequences. An nptII expression cassette was co-transferred as selectable marker followed by selection of cultures with geneticin and regeneration of plants. The integration of intact MxgPPDK4 transgenes was confirmed by PCR of sugarcane genomic DNA. Using qRT-PCR, PPDK transcript increased up to 1.5 times the level observed in non-transgenic control plants. PPDK enzyme activity and photosynthetic rates of these transgenic lines were significantly higher in MxgPPDK4 transgenic lines compared to controls. Replicated field testing in single row plots displayed a trend to increased biomass production in MxgPPDK4 lines. Our results indicate that elevating MxgPPDK4 expression improves the photosynthetic efficiency of sugarcane and may have implications for improving biomass yield which needs to be confirmed with larger field trials.
Ratna Karan,. University of Florida – IFAS, Agronomy Department, Gainesville, FL. In Vitro Cellular and Developmental Biology, 52:S40-41, 2016