Biomass Accumulation and Cell Wall Structure of Rice Plants Overexpressing a Dirigent-Jacalin of Sugarcane (ShDJ) Under Varying Conditions of Water Availability

A sugarcane gene encoding a dirigent-jacalin, ShDJ, was induced under drought stress. To elucidate its biological function, we integrated a ShDJ-overexpression construction into the rice Nipponbare genome via Agrobacterium-mediated transformation. Two transgenic lines with a single copy gene in T0 were selected and evaluated in both the T1 and T4 generations. Transgenic lines had drastically improved survival rate under water deficit conditions, at rates close to 100%, while WT did not survive. Besides, transgenic lines had improved biomass production and higher tillering under water deficit conditions compared with WT plants. Reduced pectin and hemicellulose contents were observed in transgenic lines compared with wild-type plants under both well-watered and water deficit conditions, whereas cellulose content was unchanged in line #17 and reduced in line #29 under conditions of low water availability. Changes in lignin content under water deficit were only observed in line #17. However, improvements in saccharification were found in both transgenic lines along with changes in the expression of OsNTS1/2 and OsMYB58/63 secondary cell wall biosynthesis genes. ShDJ-overexpression up-regulated the expression of the OsbZIP23, OsGRAS23, OsP5CS, and OsLea3 genes in rice stems under well-watered conditions. Taken together, our data suggest that ShDJ has the potential for improving drought tolerance, plant biomass accumulation, and saccharification efficiency

Genomic basis of sex determination and avirulence in the Hessian fly (Mayetiola destructor)

The Hessian fly, Mayetiola destructor (Say), is one of the most destructive insect pests of wheat (Triticum spp.), causing significant losses to US agriculture every year. This insect is a member of the economically important gall midge (Cecidomyiidae) family in the order Diptera. It serves as an excellent model for studying plant-insect interactions, especially those involving gene-for-gene interactions. Knowledge about the underlying molecular mechanism of these interactions in insects is still scarse, because insect avirulence (Avr) genes and their cognate resistance (R) genes have not been identified. Valuable information has been gained in the past decade in this field of study, mainly from plant-pathogen systems. The research presented in this study was focused in the two major topics related to this insect pest: (1) understanding the genomic basis of post-zygotic chromosome elimination in sex determination; and (2) test the gene-for-gene hypothesis by attempting to discover the Avr gene (vH9) that corresponds to the R gene H9 in wheat. The content of this thesis is divided into three chapters. Chapter one introduces some of the general aspects of the biology and importance of the Hessian fly. Chapter two discusses in detail the genetic and physical mapping of a genetic factor Cm (Chromosome maintenance), that has a maternal effect and controls post-zygotic chromosome elimination during sex determination. Chapter three describes the fine-scale mapping of the vH9 Avr gene within a 176 kb sequence region on the short arm of chromosome X1 and the discovery of candidate vH9 genes. The best candidate gene had polymorphisms that co-segregated with virulence to H9 and presented features resembling the Avr genes of oomycetes. The information generated from this study is expected to facilitate the discovery of new avirulence genes both in Hessian fly and in closely related insect species, contribute to the identification of the corresponding resistance gene products in the host plant, and help us to better understand the processes involved in the evolution of sex determination mechanisms in different organisms. As a consequence of this study, improved strategies to control this insect pest may be developed, and it may be possible to use diagnostics to monitor for virulence, as well as to engineer plants conferring a more efficient and durable source of resistance against the evolution of virulent genotypes

Biomass accumulation and cell wall structure of rice plants overexpressing a dirigent-jacalin of sugarcane (ShDJ) under varying conditions of water availability

A sugarcane gene encoding a dirigent-jacalin, ShDJ, was induced under drought stress. To elucidate its biological function, we integrated a ShDJ-overexpression construction into the rice Nipponbare genome via Agrobacterium- mediated transformation. Two transgenic lines with a single copy gene in T-0 were selected and evaluated in both the T-1 and T-4 generations. Transgenic lines had drastically improved survival rate under water deficit conditions, at rates close to 100%, while WT did not survive. Besides, transgenic lines had improved biomass production and higher tillering under water deficit conditions compared with WT plants. Reduced pectin and hemicellulose contents were observed in transgenic lines compared with wild-type plants under both well-watered and water deficit conditions, whereas cellulose content was unchanged in line #17 and reduced in line #29 under conditions of low water availability. Changes in lignin content under water deficit were only observed in line #17. However, improvements in saccharification were found in both transgenic lines along with changes in the expression of OsNTS1/2 and OsMYB58/63 secondary cell wall biosynthesis genes. ShDJ-overexpression upregulated the expression of the OsbZIP23, OsGRAS23, OsP5CS, and OsLea3 genes in rice stems under well-watered conditions. Taken together, our data suggest that ShDJ has the potential for improving drought tolerance, plant biomass accumulation, and saccharification efficiency10CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP552381/2007-1sem informação2011/50661-8; 2008/57495-3; 2017/24420-