The effect of heat stress on sugar beet recombination

Heating up meiosis - Chromosome recombination and segregation under high temperatures

Heat stress is one of the major constraints to plant growth and fertility. During the current climate crisis, heat waves have increased dramatically, and even more extreme conditions are predicted for the near future, considerably affecting ecosystems and seriously threatening world food security. Although heat is very well known to affect especially reproductive structures, little is known about how heat interferes with reproduction in comparison to somatic cells and tissues. Recently, the effect of heat on meiosis as a central process in sexual reproduction has been analyzed in molecular and cytological depth. Notably, these studies are not only important for applied research by laying the foundation for breeding heat-resilient crops, but also for fundamental research, revealing general regulatory mechanisms of recombination and chromosome segregation control.

Advancements and prospectives of sugar beet (Beta vulgaris L.) biotechnology

Sugar beet (Beta vulgaris L.) is the second largest sugar-producing crop (following sugarcane), accounting around 40% of total global sugar output. It has been reckoned with huge contribution in sugar, ethanol, and fodder industries. Since sugar beet is recalcitrant in nature, to address the multifaceted difficulties associated with its conventional propagation, several biotechnological tools and techniques aiming with in vitro-based mass regeneration-cum-genetic enhancement are becoming popular. The implementation of effective methodology for in vitro regeneration from ex vitro explant sources becomes the necessity for successful commercial-scale clonal propagation and genetic modification. Substantial research achievements have been made in the past few decades in connection to the optimization of in vitro protocols for direct and callus-mediated regeneration, homozygous line production, somatic hybridization, and genetic transformation of sugar beet. The current review summarizes several reported findings on various physio-chemical factors responsible for direct, indirect organogenesis, somatic embryogenesis, protoplast culture, haploid culture, acclimatization accountable for plantlet mass multiplication, assessing the genetic integrity of in vitro-cultured plantlets, and, finally, successful transgenic approaches to remediate biotic and abiotic stresses. Furthermore, this study highlights undiscovered regions, research gaps, and major bottlenecks that might be considered in developing significant innovative ideas related to sugar beet biotechnology in the near future. KEY POINTS: • Sugar beet, the second largest sugar producer, is a major contributor in sugar, ethanol, and fodder industries. • Current review comprehensively evaluates diverse factors influencing the success of in vitro biotechnological interventions. • This review further highlights the research gaps and offers way outs to attain comprehensive genetic improvement.

Comparison of meiotic transcriptomes of three maize inbreds with different origins reveals differences in cell cycle and recombination

Background

Cellular events during meiosis can differ between inbred lines in maize. Substantial differences in the average numbers of chiasmata and double-strand breaks (DSBs) per meiotic cell have been documented among diverse inbred lines of maize: CML228, a tropical maize inbred line, B73 and Mo17, temperate maize lines. To determine if gene expression might explain these observed differences, an RNA-Seq experiment was performed on CML228 male meiocytes which was compared to B73 and Mo17 male meiocytes, where plants were grown in the same controlled environment.

Results

We found that a few DSB-repair/meiotic genes which promote class I crossovers (COs) and the Zyp1 gene which limits newly formed class I COs were up-regulated, whereas Mus81 homolog 2 which promotes class II COs was down-regulated in CML228. Although we did not find enriched gene ontology (GO) categories directly related to meiosis, we found that GO categories in membrane, localization, proteolysis, energy processes were up-regulated in CML228, while chromatin remodeling, epigenetic regulation, and cell cycle related processes including meiosis related cell cycle processes were down-regulated in CML228. The degree of similarity in expression patterns between the three maize lines reflect their genetic relatedness: B73 and Mo17 had similar meiotic expressions and CML228 had a more distinct expression profile.

Conclusions

We found that meiotic related genes were mostly conserved among the three maize inbreds except for a few DSB-repair/meiotic genes. The findings that the molecular players in limiting class I CO formation (once CO assurance is achieved) were up-regulated and those involved in promoting class II CO formation were down-regulated in CML228 agree with the lower chiasmata number observed in CML228 previously. In addition, epigenetics such as chromatin remodeling and histone modification might play a role. Transport and energy-related processes was up-regulated and Cyclin13 was down-regulated in CML228. The direction of gene expression of these processes agree with that previously found in meiotic tissues compared with vegetative tissues. In summary, we used different natural maize inbred lines from different climatic conditions and have shown their differences in expression landscape in male meiocytes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08922-w.

Measuring the frequency and distribution of meiotic crossovers in homozygous barley inbred lines

We report a novel approach for establishing the number and position of CO events in individual homozygous inbred plants by combining low level EMS mutagenesis, speed breeding, whole genome shotgun sequencing and sliding window analysis of the induced molecular variant data. We demonstrate the approach by exploring CO frequency and distribution in self-fertilised progeny of the inbred barley cultivar Bowman and compare these observations to similar data obtained from a Bowman nearly isogenic line (BW230 Hvmlh3) containing a mutation in the DNA mismatch repair gene HvMLH3. We have previously shown that Hvmlh3 decreases both plant fertility and recombination by ~50%. We compare our results to those from previously published traditional genetic analysis of F3 families derived from multiple F2 lines containing WT or mutant alleles of HvMLH3, revealing a high level of correspondence between analyses. We discuss possible applications of the approach in streamlining the assessment of recombination in plant meiosis research.

Genomic prediction of the recombination rate variation in barley - A route to highly recombinogenic genotypes

Meiotic recombination is not only fundamental to the adaptation of sexually reproducing eukaryotes in nature but increased recombination rates facilitate the combination of favourable alleles into a single haplotype in breeding programmes. The main objectives of this study were to (i) assess the extent and distribution of the recombination rate variation in cultivated barley (Hordeum vulgare L.), (ii) quantify the importance of the general and specific recombination effects, and (iii) evaluate a genomic selection approach's ability to predict the recombination rate variation. Genetic maps were created for the 45 segregating populations that were derived from crosses among 23 spring barley inbreds with origins across the world. The genome-wide recombination rate among populations ranged from 0.31 to 0.73 cM/Mbp. The crossing design used in this study allowed to separate the general recombination effects (GRE) of individual parental inbreds from the specific recombination effects (SRE) caused by the combinations of parental inbreds. The variance of the genome-wide GRE was found to be about eight times the variance of the SRE. This finding indicated that parental inbreds differ in the efficiency of their recombination machinery. The ability to predict the chromosome or genome-wide recombination rate of an inbred ranged from 0.80 to 0.85. These results suggest that a reliable screening of large genetic materials for their potential to cause a high extent of genetic recombination in their progeny is possible, allowing to systematically manipulate the recombination rate using natural variation.

Effect of Temperature and Maternal Age on Recombination Rate in Cattle

Meiotic recombination is a fundamental biological process that facilitates meiotic division and promotes genetic diversity. Recombination is phenotypically plastic and affected by both intrinsic and extrinsic factors. The effect of maternal age on recombination rates has been characterized in a wide range of species, but the effect’s direction remains inconclusive. Additionally, the characterization of temperature effects on recombination has been limited to model organisms. Here we seek to comprehensively determine the impact of genetic and environmental factors on recombination rate in dairy cattle. Using a large cattle pedigree, we identified maternal recombination events within 305,545 three-generation families. By comparing recombination rate between parents of different ages, we found a quadratic trend between maternal age and recombination rate in cattle. In contrast to either an increasing or decreasing trend in humans, cattle recombination rate decreased with maternal age until 65 months and then increased afterward. Combining recombination data with temperature information from public databases, we found a positive correlation between environmental temperature during fetal development of offspring and recombination rate in female parents. Finally, we fitted a full recombination rate model on all related factors, including genetics, maternal age, and environmental temperatures. Based on the final model, we confirmed the effect of maternal age and environmental temperature during fetal development of offspring on recombination rate with an estimated heritability of 10% (SE = 0.03) in cattle. Collectively, we characterized the maternal age and temperature effects on recombination rate and suggested the adaptation of meiotic recombination to environmental stimuli in cattle. Our results provided first-hand information regarding the plastic nature of meiotic recombination in a mammalian species.