Functioning of the Photosynthetic Apparatus in Response to Drought Stress in Oat × Maize Addition Lines

The oat × maize chromosome addition (OMA) lines, as hybrids between C3 and C4 plants, can potentially help us understand the process of C4 photosynthesis. However, photosynthesis is often affected by adverse environmental conditions, including drought stress. Therefore, to assess the functioning of the photosynthetic apparatus in OMA lines under drought stress, the chlorophyll content and chlorophyll a fluorescence (CF) parameters were investigated. With optimal hydration, most of the tested OMA lines, compared to oat cv. Bingo, showed higher pigment content, and some of them were characterized by increased values of selected CF parameters. Although 14 days of drought caused a decrease of chlorophylls and carotenoids, only slight changes in CF parameters were observed, which can indicate proper photosynthetic efficiency in most of examined OMA lines compared to oat cv. Bingo. The obtained data revealed that expected changes in hybrid functioning depend more on the specific maize chromosome and its interaction with the oat genome rather than the number of retained chromosomes. OMA lines not only constitute a powerful tool for maize genomics but also are a source of valuable variation in plant breeding, and can help us to understand plant susceptibility to drought. Our research confirms more efficient functioning of hybrid photosynthetic apparatus than oat cv. Bingo, therefore contributes to raising new questions in the fields of plant physiology and biochemistry. Due to the fact that the oat genome is not fully sequenced yet, the mechanism of enhanced photosynthetic efficiency in OMA lines requires further research.

3-D Nucleus Architecture in Oat × Maize Addition Lines

The nucleus architecture of hybrid crop plants is not a well-researched topic, yet it can have important implications for their genetic stability and usefulness in the successful expression of agronomically desired traits. In this work we studied the spatial distribution of introgressed maize chromatin in oat × maize addition lines with the number of added maize chromosomes varying from one to four. The number of chromosome additions was confirmed by genomic in situ hybridization (GISH). Maize chromosome-specific simple sequence repeat (SSR) markers were used to identify the added chromosomes. GISH on 3-D root and leaf nuclei was performed to assess the number, volume, and position of the maize-chromatin occupied regions. We revealed that the maize chromosome territory (CT) associations of varying degree prevailed in the double disomic lines, while CT separation was the most common distribution pattern in the double monosomic line. In all analyzed lines, the regions occupied by maize CTs were located preferentially at the nuclear periphery. A comparison between the tissues showed that the maize CTs in the leaf nuclei are positioned closer to the center of the nucleus than in the root nuclei. These findings shed more light on the processes that shape the nucleus architecture in hybrids.

Development of an amenable system for site-specific addition to a maize chromosome

Currently, transgenic maize is produced by random integration of a transgenes into the plant. This works for single genes, but not as well for multiple traits. Identifying plants that contain several transgenes becomes a very difficult task. Gene stacking at a single location in the genome would make combining multiple transgenes into plants a simpler process. This project focused on the development of a system would allow for transgenes to be sequentially added to a specific site in the maize genome. The system utilizes two recombinases, Cre recombinase and _C31 Integrase, to remove a selectable marker and to integrate transgenes. An initial construct containing a selectable marker, flanked by LoxP sites, which are acted upon by Cre recombinase, and an attP site, were transformed. The selectable marker was then removed from the integrated transgene by exposure to Cre recombinase. Two amendment constructs enable modification of the integrated construct by utilizing complementary attP and attB sites, which are acted upon by _C31 Integrase. The amendment constructs contain cargo and a promoterless selectable marker which, upon successful recombination with the target site, restores expression of the selectable marker. Successful demonstration of this system simplifies generation of multi-transgene plants, and the assembly of multi-gene pathways in plants.

Genetic analysis of oleic acid content in the oils of maize sugary-2 mutants

Aim. Genetic analysis of oleate content in the carriers of maize mutation su2. Methods. Experiments were performed on a series of unrelated inbreeds – carriers of mutation su2 which were hybridized by the diallel and top – cross crossings. The analysis of the fatty acid composition of oil were carried out using a modified gas-chromatographic Peyskare method. Results. It was found, that su2 mutants were notable as having the increased content of oleate compared to the maize of usual type and this trait has a quantitative nature. The inbreeds – carriers of su2 mutation were significantly differed in the the effects of combining abilities for the oleate content. The inheritance of oleate was carried out by the type of incomplete dominance with the prevailing contribution of additive effects to the variance. Conclusions. In the sixth maize chromosome it is very likely that there is a spatial linkage of the su2 and oleate- encoding locus, the effect of which can be modified by the polygenic complex. Keywords: Zea mays L., mutation su2, oleic acid, genetic analysis.