Plant Biology Seminar - Two speakers from the University of York.

Identification of novel players in rice salt-stress responses using CRISPR/Cas genome editing

Tuesday 5 June 2018, 1.00pm

Speaker: Raquel Carvalho 

A large amount of arable land is affected by soil salinity, a major cause of crop yield reduction worldwide. Rice, an important food crop feeding more than half of the world, is highly susceptible to salinity stress. Unravelling key players in the complex molecular networks responsible for rice salt-tolerance is crucial to both breeding and engineering of improved salt tolerant rice.

Candidate genes for salt tolerance were identified from a salinity GWAS in our lab. Twenty-nine genes were found to be common to all salinity treatments. Interestingly, all localized to a specific region of chromosome eight, overlapping with quantitative trait loci previously reported to be important for salinity tolerance in rice. Thus, the yet uncharacterized candidate genes in this region are highly likely to affect rice salt stress.

In order to assess the relevance of these high confidence candidate genes, we are characterizing knockout mutants for selected genes. We have used CRISPR/Cas genome editing to introduce deletions in the coding regions of each gene. Here we show the successful isolation of mutants for two candidate genes. The first one, OsWAKL2 (Wall-Associated Kinase-Like2), belongs to the large family of plasma membrane receptor-like kinases (RLKs), regarded as potential cell wall “sensors”. Interestingly, expression patterns in salt sensitive and tolerant rice cultivars shows that OsWAKL2 is expressed in the sensitive lines only. The second gene, OsUGE2, encodes a putative Uridine-diphospho-(UDP)-Glucose/Galactose 4-Epimerase. Expression of OsUGE2 is induced by salt treatment in different rice cultivars tested. Homozygous knockout mutants for each gene will be phenotyped under salinity stress conditions. 

Location: K018

Email: luke.mackinder@york.ac.uk 

The requirement for calcification differs between ecologically important coccolithophore species 

Tuesday 5th June 2018, 1.00pm

Speaker: Charlotte E. Walker, Alison R. Taylor, Gerald Langer, Grażyna M. Durak, Sarah Heath, Ian Probert, Toby Tyrrell, Colin Brownlee and Glen L.Wheeler

Coccolithophores are globally distributed unicellular marine algae that are characterised by a covering of calcite coccoliths. Calcification by coccolithophores contributes significantly to global biogeochemical cycles. However, the physiological requirement for calcification remains poorly understood as non-calcifying strains of some commonly used model species, such as Emiliania huxleyi, grow normally in laboratory culture. 

To determine whether the requirement for calcification differs between coccolithophore species, we utilised multiple independent methodologies to disrupt calcification in two important species of coccolithophore, Emiliania huxleyi and Coccolithus braarudii. We investigated their physiological response and used time-lapse imaging to visualise the processes of calcification and cell division in individual cells. 

Disruption of calcification resulted in major growth defects in C. braarudii, but not in E. huxleyi. We find no evidence that calcification supports photosynthesis in C. braarudii but show that an inability to maintain an intact coccosphere results in cell cycle arrest. 

We find that C. braarudii is very different from E. huxleyi as it exhibits an obligate requirement for calcification. The identification of a growth defect in C. braarudii resulting from disruption of the coccosphere may be important in considering their response to future changes in ocean carbonate chemistry.