Photosynthetic traits of Australian wild rice (Oryza australiensis) confer tolerance to extreme daytime temperatures

Key message A wild relative of rice from the Australian savannah was compared with cultivated rice, revealing thermotolerance in growth and photosynthetic processes and a more robust carbon economy in extreme heat. Abstract Above ~ 32 °C, impaired photosynthesis compromises the productivity of rice. We compared leaf tissues from heat-tolerant wild rice (Oryza australiensis) with temperate-adapted O. sativa after sustained exposure to heat, as well as diurnal heat shock. Leaf elongation and shoot biomass in O. australiensis were unimpaired at 45 °C, and soluble sugar concentrations trebled during 10 h of a 45 °C shock treatment. By contrast, 45 °C slowed growth strongly in O. sativa. Chloroplastic CO2 concentrations eliminated CO2 supply to chloroplasts as the basis of differential heat tolerance. This directed our attention to carboxylation and the abundance of the heat-sensitive chaperone Rubisco activase (Rca) in each species. Surprisingly, O. australiensis leaves at 45 °C had 50% less Rca per unit Rubisco, even though CO2 assimilation was faster than at 30 °C. By contrast, Rca per unit Rubisco doubled in O. sativa at 45 °C while CO2 assimilation was slower, reflecting its inferior Rca thermostability. Plants grown at 45 °C were simultaneously exposed to 700 ppm CO2 to enhance the CO2 supply to Rubisco. Growth at 45 °C responded to CO2 enrichment in O. australiensis but not O. sativa, reflecting more robust carboxylation capacity and thermal tolerance in the wild rice relative.

Allelic variation for alpha-Glucan Water Dikinase is associated with starch phosphate content in tetraploid potato

Key message Association analysis resulted in the identification of specific StGWD alleles causing either an increase or decrease in starch phosphate content which was verified in diploid and tetraploid potato mapping populations. Abstract Potatoes are grown for various purposes like French fries, table potatoes, crisps and for their starch. One of the most important aspects of potato starch is that it contains a high amount of phosphate ester groups which are considered to be important for providing improved functionalization after derivatization processes. Little is known about the variation in phosphate content as such in different potato varieties and thus we studied the genetic diversity for this trait. From other studies it was clear that the phosphate content is controlled by a quantitative trait locus (QTL) underlying the candidate gene α-Glucan Water Dikinase (StGWD) on chromosome 5. We performed direct amplicon sequencing of this gene by Sanger sequencing. Sequences of two StGWD amplicons from a global collection of 398 commercial cultivars and progenitor lines were used to identify 16 different haplotypes. By assigning tag SNPs to these haplotypes, each of the four alleles present in a cultivar could be deduced and linked to a phosphate content. A high value for intra-individual heterozygosity was observed (Ho = 0.765). The average number of different haplotypes per individual (Ai) was 3.1. Pedigree analysis confirmed that the haplotypes are identical-by-descent (IBD) and offered insight in the breeding history of elite potato germplasm. Haplotypes originating from introgression of wild potato accessions carrying resistance genes could be traced. Furthermore, association analysis resulted in the identification of specific StGWD alleles causing either an increase or decrease in starch phosphate content varying from 12 nmol PO4/mg starch to 38 nmol PO4/mg starch. These allele effects were verified in diploid and tetraploid mapping populations and offer possibilities to breed and select for this trait.

Large-scale comparative transcriptomic analysis of temperature-responsive genes in Arabidopsis thaliana

Key message Comparative transcriptomic analysis provides broad and detailed understandings of transcriptional responses to a wide range of temperatures in different plant tissues, and unique regulatory functions of temperature-mediating transcription factors. Abstract Climate change poses a great threat to plant diversity and food security. It is thus of necessity to understand the molecular mechanisms for perceiving and responding to adverse temperature changes, to develop the cultivars that are resilient to these environmental stresses. Making use of publicly available datasets, we gathered and re-analyzed 259 individual transcriptomic profiles from 139 unique experiments of Arabidopsis thaliana’s shoot, root, and seedling tissues, subjected to a wide variety of temperature conditions, ranging from freezing, cold, low and high ambient temperatures, to heat shock. Despite the underlying differences in the overall transcriptomic profiles between the plant tissues, we were able to identify distinct sets of genes whose transcription patterns were highly responsive to different types of temperature conditions, some were common among the tissues and some were tissue-specific. Interestingly, we observed that the known temperature-responsive genes such as the heat-shock factor (HSF) family, were up-regulated not only in response to high temperatures, but some of its members were also likely involved in the cold response. By integrating the DNA-binding specificity information of the key temperature transcription factor (TF) HSFA1a, PIF4, and CBFs, we elucidated their distinct DNA-binding patterns to the target genes that showed different transcriptional responses. Taken together, we have comprehensively characterized the transcription patterns of temperature-responsive genes and provided directly testable hypotheses on the regulatory roles of key temperature TFs on the expression dynamics of their target genes.