Author: Arkadiusz Kosmala
Institute of Plant Genetics, Polish Academy of Sciences, Poznań
Dr. Arkadiusz Kosmala leads a team studying the cytogenetics and molecular physiology of grasses at the Department of Environmental Stress Biology of the PAS Institute of Plant Genetics in Poznań. In 2013, the team was awarded the Prize of PAS Division II: Biological and Agricultural Sciences for its research into molecular mechanisms of abiotic stress tolerance in Lolium and Festuca grasses.
The Central and Eastern European region, including Poland, is dominated by a temperate continental climate. Low temperatures in January and February, and occasional frosts in March, have a negative impact on crop yields. This is made worse by frequent periods of high temperatures and very low rainfall in summer. Soil droughts in certain regions of Poland (such as Wielkopolska) can damage as much as 70% of crops. Making the most of the potential of fodder grasses as the main vegetation component of grasslands (meadows and pastures) is therefore contingent on not just improving plant yield and quality, but also on the degree of stress tolerance to drought and low temperatures that can be achieved through selective breeding of different species and varieties.
All things considered, ryegrasses and fescues should be regarded as offering an excellent avenue for basic research and crop breeding efforts aiming to develop new, high-yield varieties able to tolerate different types of environmental stress.
The two most important fodder species of ryegrass – Italian ryegrass (Lolium multiflorum) and perennial ryegrass (Lolium perenne) – are high-yield grasses, producing dry green leaves containing high levels of soluble, easily digestible carbohydrates. Unfortunately, however, they have a low tolerance for abiotic and biotic stresses. Fescue species, including meadow fescue (Festuca pratensis) and tall fescue (Festuca arundinacea), do have high tolerance to low temperatures, drought, and high soil salinity, yet their quality as fodder is lower than that of ryegrasses. Interestingly, however, these species can cross-pollinate to create new varieties; many remain fertile since the chromosomes of the parental species conjugate and recombine freely. This means it is possible to hybridize different varieties to bring together the best qualities in a single new genotype.
This can be achieved through amphiploidization, where the complete genomes of two parent species are combined, doubling the number of chromosomes (using colchicine) in the new hybrid, or through introgression, whereby genetic information is transferred from one species to another through hybridization and backcrossing. Ryegrass and fescue species are used to obtain diploid and polyploid hybrids (containing two or more pairs of chromosomes) and then to create amphiploid and/or introgressive forms, known as Festulolium. Festuca arundinacea provides genes for high tolerance of drought and low temperatures, while Festuca pratensis is the main source of genes for frost tolerance.
The way a plant responds to stress factors on the molecular level can be analyzed by studying the expression of selected genes, accumulation of certain proteins, and the functioning of the physiological parameters of the photosynthesis mechanism. Our unit studying the cytogenetics and molecular physiology of grasses at the PAS Institute of Plant Genetics has been engaged in such research for many years. Studies focus on describing certain elements of meadow fescue’s response to low temperatures and tall fescue’s response to drought using physiological analysis, such as measurements of relative water content in the leaves, electrolyte leakage, water absorption, chlorophyll fluorescence parameters, gas exchange (transpiration and intensity of photosynthesis), and proteomic analysis using 2D electrophoresis and mass spectrometry.
In many plant species, including grasses, frost tolerance can be induced by acclimation to low temperatures. Molecular research has been able to identify proteins that accumulate at different levels during frost treatment in meadow fescue genotypes exhibiting differing stress tolerance potential. These include phosphoglycerate kinase and RuBisCo activase beta – enzymes that play a part in the Calvin cycle and the process of CO2 assimilation during photosynthesis. We have also identified chloroplast proteins which showed different accumulation levels under water-shortage conditions and/or following irrigation in genotypes of tall fescue with a different drought tolerance potential. These include metalloprotease FTSH2, cyclophilin CYP38, fibrillin and lipocalin – proteins involved in the protection of structures responsible for photosynthesis against the effects of water shortage. The levels of accumulation of these proteins in fescues may also turn out to be key for the potential of abiotic stress tolerance in ryegrasses.
Alongside the model plant species described here, introgression Festulolium forms offer excellent material for studying the molecular basis of environmental stress tolerance. On one hand, they are characterized by the same genetic background, while on the other they may represent different responses to the same stress factor. In the context of describing cellular responses to stress caused by drought, our research using tetraploid introgression forms of Italian ryegrass with tall fescue genes is worthy of note. We have discovered a mechanism regulating photosynthesis intensity under drought conditions, independent of the degree of stomata opening although likely linked with the intensity of the Calvin cycle and the degree of accumulation of chloroplast aldolase.
Festulolium forms are also a fascinating model for cytogenetics research, for example mapping chromosome segments containing genes for desirable characteristics such as high tolerance of abiotic stresses. Using genomic in situ hybridization (GISH) and fluorescence in situ hybridization (FISH) with rDNA probes to study the short arm of chromosome 2, we have identified certain genes linked to winter hardiness and frost tolerance in diploid introgressive forms of Italian ryegrass with meadow fescue or tall fescue genes.
…and for breeding
Transferring genes for agriculturally significant characteristics between ryegrass and fescue species, using either amphiploidization or introgression, is widely used in breeding programs. Research into gene transfer between ryegrass and fescue species and successful breeding is the subject of ongoing collaboration between the PAS Institute of Plant Genetics, the Szelejewo Plant Breeding company (now DANKO Plant Breeding, Szelejewo Branch), and the Faculty of Plant Physiology at the University of Agriculture in Kraków. The hybrids, in particular tetraploid hybrids of meadow fescue and Italian ryegrass (Festuca pratensis × Lolium multiflorum), have been used to develop numerous varieties of Festulolium; four amphiploid varieties (Felopa, Sulino, Rakopan and Agula) have been developed in Poland.
Homologous chromosomes of ryegrasses and fescues are able to conjugate in metaphase I of meiosis; however, they are sufficiently different from one another to be identifiable in hybrids and their amphiploid and introgression derivatives using GISH. Analysis of genomic structures of selected amphiploid Festulolium forms in successive generations has revealed a high degree of homologous recombination and a dominance of the ryegrass genome over that of the fescue. It is likely that this may be one of the reasons for the genetic instabilities frequently observed among distant hybrids.
Our research shows that introgression of selected fescue genes into ryegrass through backcrossing of the hybrid with a diploid or tetraploid ryegrass parent form may be a very effective way of obtaining stable and sufficiently fertile genotypes with a higher potential for environmental stress tolerance. Collaboration between DANKO (Szelejewo Branch) and the Faculty of Plant Physiology at the University of Agriculture in Kraków has resulted in the development of successful introgression forms of Italian ryegrass: diploid, with meadow fescue or tall fescue genes with a significantly higher degree of frost resistance, and tetraploid, with tall fescue genes featuring a significantly higher drought tolerance potential in comparison with existing diploid/tetraploid varieties of Italian ryegrass. These introgression forms have been included in breeding programs with the aim of introducing new varieties of Italian ryegrass with improved parameters of abiotic stress tolerance.
Further reading:Ghesquire M., Humphreys M.W., Zwierzykowski Z. (2010). Festulolium. In: B. Boller, U.K. Posselt and F. Veronesi (eds.), Fodder Crops and Amenity Grasses. pp. 288-311. Series: Handbook of Plant Breeding, Vol. 5. Springer Science+Business Media.
Kosmala A., Bocian A., Rapacz M., Jurczyk B., Zwierzykowski Z. (2009). Identification of leaf proteins differentially accumulated during cold acclimation between Festuca pratensis plants with distinct levels of frost tolerance. Journal of Experimental Botany, 60, 3595-3609.
Kosmala A., Perlikowski D., Pawłowicz I., Rapacz M. (2012). Changes in the chloroplast proteome following water deficit and subsequent watering in a high and a low drought tolerant genotype of Festuca arundinacea. Journal of Experimental Botany, 63, 6161-6172.
© Academia 2 (42) 2014