Stress-induced expression of IPT gene in transgenic wheat reduces grain yield penalty under drought.

BACKGROUND: The heterologous expression of isopentenyl transferase (IPT) under the transcriptional control of the senescence-associated receptor-like kinase (SARK) promoter delayed cellular senescence and, through it, increased drought tolerance in plants. To evaluate the effect of pSARK::IPT expression in bread wheat, six independent transgenic events were obtained through the biolistic method and evaluated transgene expression, phenology, grain yield and physiological biomass components in plants grown under both drought and well-irrigating conditions. Experiments were performed at different levels: (i) pots and (ii) microplots inside a biosafety greenhouse, as well as under (iii) field conditions. RESULTS: Two transgenic events, called TR1 and TR4, outperformed the wild-type control under drought conditions. Transgenic plants showed higher yield under both greenhouse and field conditions, which was positively correlated to grain number (given by more spikes and grains per spike) than wild type. Interestingly, this yield advantage of the transgenic events was observed under both drought and well-watered conditions. CONCLUSIONS: The results obtained allow us to conclude that the SARK promoter-regulated expression of the IPT gene in bread wheat not only reduced the yield penalty produced by water stress but also led to improved productivity under well-watered conditions.

Water deficit stress tolerance in maize conferred by expression of an isopentenyltransferase (IPT) gene driven by a stress- and maturation-induced promoter.

Senescence can be delayed in transgenic plants overexpressing the enzyme isopentenyltransferase (IPT) due to stress-induced increased levels of endogenous cytokinins. This trait leads to sustained photosynthetic activity and improved tolerance to abiotic stress. The aim of this study was to generate and characterize transgenic plants of maize (Zea mays L.) transformed with the IPT gene sequence under the regulation of SARK promoter (protein kinase receptor-associated senescence). Three independent transgenic events and their segregating null controls were evaluated in two watering regimes (WW: well watered; WD: water deficit) imposed for two weeks around anthesis. Our results show that the WD treatment induced IPT expression with the concomitant increase in cytokinin levels, which prolonged the persistence of total green leaf area, and maintained normal photosynthetic rate and stomatal conductance. These trends were accompanied by a minor decrease in number of grains per plant, individual grain weight and plant grain yield as compared to WW plants. Plants expressing the IPT gene under WD had PGR, anthesis and silking dates and biomass levels similar to WW plants. Our results demonstrate that expression of the IPT gene under the regulation of the SARK promoter helps improve productivity under WD conditions in C4 plants like maize.

Microsatellite isolation and characterization in sunflower (Helianthus annuus L.).

Development of microsatellite markers for sunflower (Helianthus annuus L.) was performed to estimate their frequency, nature (structure), levels of polymorphism, usefulness for genotype identification, and calculation of genetic relationships between inbred lines representing the species diversity. Isolation was performed from a small-insert genomic library followed by hybridization screening using oligonucleotide probes containing different nucleotide arrays. In this work, 503 unique microsatellite clones were sequenced and 271 PCR primer sequences bordering the microsatellite repeat were designed. For polymorphism assessment, 16 H. annuus germplasm accessions were checked and 170 of the primers tested were shown to be polymorphic for the selected lines. The polymorphic microsatellites produced an average of 3.5 alleles/locus and an average polymorphism information content (PIC) of 0.55. The most frequently found motifs within polymorphic simple-sequence repeats (SSRs) were: (GA)n, (GT)n, (AT)n, followed by trinucleotides (ATT)n, (TGG)n, and (ATC)n, and the tetranucleotide (CATA)n. Most of the 170 SSRs obtained showed important differences in the 16 reference inbred lines used for their characterization. In this work, 20 of the most informative SSRs destined to sunflower genotyping and legal fingerprinting purposes are fully described.