Legumes underpin the global food network, providing the majority of the world’s dietary protein.
However, global productivity of grain legumes is limited by environmental stresses, particularly
chilling and freezing. For example, chilling temperatures (0-15 ºC) limit the production of soybean
(Glycine max; a tropical legume), while extreme freezing temperatures (<0 ºC) limit use of temperate
legumes such as faba bean (Vicia faba L). The following studies were performed to gain new insights
into chilling and freezing tolerance in these two important legumes. Transgenic soybean lines,
overexpressing the rice cysteine protease inhibitor, oryzacystatin I (OCI), showed decreased chillinginduced
inhibition of photosynthesis compared to wild type (Wt). These lines also showed an
increased abundance of transcripts encoding the strigolactone (SL) biosynthesis enzymes: carotenoid
cleavage dioxygenases 7 and 8 (CCD7, CCD8). Pea (rms3, rms4, rms5) and Arabidopsis thaliana
(max2-1, max3-9, max4-1) mutants, deficient in SL synthesis and signalling, showed enhanced
sensitivity to dark-chilling. Differences in chilling and freezing sensitivity were also identified in 5
faba bean cultivars. Transcriptome profiling comparisons were performed on the most chilling
sensitive (Wizard) and most chilling tolerant (Hiverna) cultivars to identify specific differences in
gene expression, underpinning stress tolerance. Moreover, genome sequencing of the Wizard cultivar
enabled the assembly and annotation of the mitochondrial and chloroplast genomes. Single nucleotide
polymorphisms (SNP) were found in several organelle genes, when comparing read sequences to
published references. Furthermore, based on published SNP orientated linkage maps, contiguous read
sequences could be mapped to chromosomal loci, leading to the identification of 8 putative nuclear
gene sequences and an increase in sequence length data at 147 loci. Together with these new genomic
resources, the discovery that cysteine proteases, phytocystatins and SL are important in legume low
temperature tolerance will enable the development of stress tolerance markers, for use in faba bean
selective breeding programs.
