Genetic Dissection of Mature Root Characteristics by Genome-Wide Association Studies in Rapeseed (Brassica napus L.)

Roots are complicated quantitative characteristics that play an essential role in absorbing water and nutrients. To uncover the genetic variations for root-related traits in rapeseed, twelve mature root traits of a Brassica napus association panel were investigated in the field within three environments. All traits showed significant phenotypic variation among genotypes, with heritabilities ranging from 55.18% to 79.68%. Genome-wide association studies (GWAS) using 20,131 SNPs discovered 172 marker-trait associations, including 103 significant SNPs (−log10 (p) > 4.30) that explained 5.24–20.31% of the phenotypic variance. With the linkage disequilibrium r2 > 0.2, these significant associations were binned into 40 quantitative trait loci (QTL) clusters. Among them, 14 important QTL clusters were discovered in two environments and/or with phenotypic contributions greater than 10%. By analyzing the genomic regions within 100 kb upstream and downstream of the peak SNPs within the 14 loci, 334 annotated genes were found. Among these, 32 genes were potentially associated with root development according to their expression analysis. Furthermore, the protein interaction network using the 334 annotated genes gave nine genes involved in a substantial number of interactions, including a key gene associated with root development, BnaC09g36350D. This research provides the groundwork for deciphering B. napus’ genetic variations and improving its root system architecture.

Distinct changes in mature root and growing root tip proteomes underlie physiological responses of bread wheat to salinity stress

The impact of salinity on wheat plants is often studied by analysis of shoot responses, even though the main mechanism of tolerance is shoot Na+ exclusion. There is a need to understand the molecular responses of root tissues that directly experience rising NaCl concentrations. We have combined analysis of root growth, ion content and respiration with proteome responses in wheat root tip and mature root tissues under saline conditions. We find significant changes in translation and protein synthesis, energy metabolism and amino acid metabolism in a root tissue specific manner. Translation and protein synthesis related proteins showed significant decreases in abundance only in root tips, as did most of the glycolytic enzymes and selected TCA cycle enzymes and ATP synthase subunits. This selective root tip proteome response indicates protein synthesis capacity and energy production were impaired under salt stress, correlating with the anatomical response of roots and reduced root tip respiration rate. Wheat roots respond directly to soil salinity, therefore shoot responses such as reduction in shoot growth and photosynthetic capacity need to be considered in light of these effects.

Oxygen in the air and oxygen dissolved in the floodwater both sustain growth of aquatic adventitious roots in rice

Flooding is an environmental stress that leads to a shortage of O2 that can be detrimental for plants. When flooded, deepwater rice grow floating adventitious roots to replace the dysfunctional soil-borne root system, but the features that ensure O2 supply and hence growth of aquatic roots have not been explored. We investigate the sources of O2 in aquatic adventitious roots and relate aerenchyma and barriers for gas diffusion to local O2 gradients, as measured by microsensor technology, to link O2 distribution in distinct root zones to their anatomical features. The mature root part receives O2 exclusively from the stem. It has aerenchyma that, together with suberin and lignin depositions at the water–root and cortex–stele interfaces, provides a path for longitudinal O2 movement toward the tip. The root tip has no diffusion barriers and receives O2 from the stem and floodwater, resulting in improved aeration of the root tip over mature tissues. Local formation of aerenchyma and diffusion barriers in the mature root channel O2 towards the tip which also obtains O2 from the floodwater. These features explain aeration of floating roots and their ability to grow under water.

Root phenotypes of young wheat plants grown in controlled environments show inconsistent correlation with mature root traits in the field

Using a field to lab approach, mature deep-rooting traits in wheat were correlated to root phenotypes measured on young plants from controlled conditions. Mature deep-rooting root traits of 20 wheat genotypes at maturity were established via coring in three field trials across 2 years. Field traits were correlated to phenotypes expressed by the 20 genotypes after growth in four commonly used lab screens: (i) soil tubes for root emergence, elongation, length, and branching at four ages to 34 days after sowing (DAS); (ii) paper pouches 7 DAS and (iii) agar chambers for primary root (PR) number and angles at 8 DAS; and (iv) soil baskets for PR and nodal root (NR) number and angle at 42 DAS. Correlations between lab and field root traits (r2=0.45–0.73) were highly inconsistent, with many traits uncorrelated and no one lab phenotype correlating similarly across three field experiments. Phenotypes most positively associated with deep field roots were: longest PR and NR axiles from the soil tube screen at 20 DAS; and narrow PR angle and wide NR angle from soil baskets at 42 DAS. Paper and agar PR angles were positively and significantly correlated to each other, but only wide outer PRs in the paper screen correlated positively to shallower field root traits. NR phenotypes in soil baskets were not predicted by PR phenotypes in any screen, suggesting independent developmental controls and value in measuring both root types in lab screens. Strong temporal and edaphic effects on mature root traits, and a lack of understanding of root trait changes during plant development, are major challenges in creating controlled-environment root screens for mature root traits in the field.

Auto-transplantation of teeth: Our Experience

Background & Objectives: To evaluate success rate of auto-transplantation of teeth with immature and mature root apex.Materials & Methods: Fifteen consecutively auto-transplanted teeth ( six with immature apex and nine with mature apex ) were followed up for a mean duration of 8.6 months and assessed for post transplant mobility, root resorption, root growth and pain. The transplanted teeth were assessed clinically and Intraoral periapical radiographs (IOPAR) were taken every three months.Results: Overall success rate was 73.3%. Higher success rate was observed for teeth with immature apex as compared to teeth with mature apex.Conclusion: Auto-transplantation can be used as reliable method for replacement of missing teeth if proper case selection and surgical protocol is followed.

Wheats developed for high yield on stored soil moisture have deep vigorous root systems

Many rainfed wheat production systems are reliant on stored soil water for some or all of their water inputs. Selection and breeding for root traits could result in a yield benefit; however, breeding for root traits has traditionally been avoided due to the difficulty of phenotyping mature root systems, limited understanding of root system development and function, and the strong influence of environmental conditions on the phenotype of the mature root system. This paper outlines an international field selection program for beneficial root traits at maturity using soil coring in India and Australia. In the rainfed areas of India, wheat is sown at the end of the monsoon into hot soils with a quickly receding soil water profile; in season water inputs are minimal. We hypothesised that wheat selected and bred for high yield under these conditions would have deep, vigorous root systems, allowing them to access and utilise the stored soil water at depth around anthesis and grain-filling when surface layers were dry. The Indian trials resulted in 49 lines being sent to Australia for phenotyping. These lines were ranked against 41 high yielding Australian lines. Variation was observed for deep root traits e.g. in eastern Australia in 2012, maximum depth ranged from 118.8 to 146.3 cm. There was significant variation for root traits between sites and years, however, several Indian genotypes were identified that consistently ranked highly across sites and years for deep rooting traits.