Heat shock proteins (HSPs) are expressed in response to environmental stresses. Compared to other kingdoms, plant HSP families are larger, presumably the result of adaptation to a wide range of stresses. Following on an analysis of drought stress characteristics in loblolly pine (Watkinson et al., 2003), expression patterns of HSP gene expression during photosynthetic acclimation were examined. One cycle of mild (-1Mpa) followed by two cycles of severe stress (-1.7Mpa) were probed for conditioning effects. Photosynthetic acclimation occurred after the first cycle. No acclimation occurred without the first mild cycle. Microarray/RT-PCR analyses showed that a pine homolog to GRP94 (ER-resident HSP90) was up-regulated after rehydration coincident with acclimation. This GRP94 is closely related to GRP94 from the desiccation tolerant plant X. viscosa, supporting the importance of this gene during acclimation to water deficit. HSP genes whose products localized to the mitochondrion showed gradual up-regulation after consecutive cycles of severe drought. The Arabidopsis pine GRP94 homolog, (AtHSP90-7) was then analyzed, using bioinformatics (Pati et al., 2006) and laboratory tools. Genes encoding putative candidate co-chaperones for GRP94 and other HSP90s were discovered, which contained water stress-related cis-elements. Arabidopsis (Col-0) wild type and two T-DNA insertion mutants in HSP90-7 were used to study the importance of this gene for photosynthetic acclimation. Only the mutants were able to acclimate to drought stress, with the level of AtHSP90-7 expression in the mutants being reduced compared to the wild type. AtHSP90-7 may have a different role in Arabidopsis, and its reduced expression activated other protective genes (Klein et al., 2006). Responses to extreme drought in resistant (Sullu) and susceptible (Negra Ojosa) lines of Andean potatoes were also compared in order to identify relationships between HSPs gene expression, and tolerance, defined as the ability to maintain photosynthesis at 50% after 25 days of drought and to recover from the stress. Tolerance was correlated with up-regulation of HSPs (mostly chaperonins) and antioxidant genes all of whose gene products are located in the chloroplast. / Ph. D.

Fe biofortification of potato is a promising strategy to prevent Fe deficiency worldwide either through traditional breeding or biotechnological approaches. These approaches require the identification of candidate genes to uptake, transport and store Fe in potato tubers. We employed multiple approaches including SNP genotyping, QTL analysis, identifying genes orthologous to Arabidopsis ferrome, yeast complementation assay and genetic transformation to avoid the limitation from a single approach. We revealed several candidate genes potentially associated with potato plant Fe acquisition, PGSC0003DMG400024976 (metal transporter), PGSC0003DMG400013297 (oligopeptide transporter), PGSC0003DMG400021155 (IRT1) and IRTunannotated (an ortholog to the IRT gene that is not annotated in the potato genome). The microorganisms in the rhizosphere react intensely with the various metabolites released by plant roots in a variety of ways such as positive, negative, and neutral. These interactions can influence the uptake and transport of micronutrients in the plant roots. Therefore, the contribution of soil microorganisms in the rhizosphere to improve Fe supply of plants may play a key role in Fe biofortification, especially under real world field-based soil scenarios. We thus investigated rhizosphere microbial community diversity in Andean potato landraces to understand the role of plant-microbial interaction in potato Fe nutrient cycling. From the analysis of the high-throughput Illumina sequences of 16S and ITS region of ribosomal RNA gene, we found that both potato landraces with low and high Fe content in tubers and a landrace on which low or high Fe content fertilizer was applied to the leaf surface had large impacts on the rhizosphere fungal community composition. Indicator species analysis (ISA) indicated that Operational Taxonomic Units (OTUs) contributing most to these impacts were closely related to Eurotiomycetes and Leotiomycetes in the phylum Ascomycota, Glomeromycetes in the phylum Glomeromycota and Microbotryomycetes in the phylum Basidiomycota. Lots of species from these groups have been shown to regulate plant mineral nutrient cycling. Our research revealed potential candidate genes and fungal taxa involved in the potato plant Fe nutrient dynamics, which provides new insights into crop management and breeding strategies for sustainable Fe fortification in agricultural production. / Ph. D.