Natural variation and gene regulatory basis for the responses of asparagus beans to soil drought

Abstract

Asparagus bean (Vigna unguiculata ssp. sesquipedalis) is the Asian subspecies of cowpea, a drought-resistant legume crop native to Africa. In order to explore the genetic variation of drought responses in asparagus bean, we conducted multi-year phenotyping of drought resistance traits across the Chinese asparagus bean mini-core. The phenotypic distribution indicated that the ssp. sesquipedalis subgene pool has maintained high natural variation in drought responses despite known domestic bottleneck. Thirty-nine SNP loci were found to show an association with drought resistance via a genome-wide association study (GWAS). Whole-plant water relations were compared among four genotypes by lysimetric assay. Apparent genotypic differences in transpiration patterns and the critical soil water threshold in relation to dehydration avoidance were observed, indicating a delicate adaptive mechanism for each genotype to its own climate. Microarray gene expression analyses revealed that known drought resistance pathways such as the ABA and phosphate lipid signaling pathways are conserved between different genotypes, while differential regulation of certain aquaporin genes and hormonal genes may be important for the genotypic differences. Our results suggest that divergent sensitivity to soil water content is an important mechanism configuring the genotypic specific responses to water deficit. The SNP markers identified provide useful resources for marker-assisted breeding.

Measurement of transpiration restriction under high vapor pressure deficit for sorghum mapping population parents

“…The donor parent of these RILs, S35 and SP2417 was VPD sensitive, and it shows that donor parent could conserve soil moisture when midday VPD was high. Similar kind of experimental data was also obtained by Vadez et al (2015) in VPD sensitive and insensitive sorghum, mapping population parents of PRLT and H77 pearl millet and cowpea genotypes; Xu et al (2015) identified the genotypic variation in transpiration pattern during mid-day in vigna unguiculate species. The restriction in transpiration under high VPD allowed by partial stomata closure saves soil moisture at the early vegetative stage, which can increase moisture availability for reproductive stages under the rainfed condition and can enhance yield (Richards and Passioura 1989;Sinclair et al 2005).…”

Variation in relative water content, proline accumulation and stress gene expression in two cowpea landraces under drought

“…Five quantitative trait loci related to drought and senescence physiology have been identified by studying the natural variation in local cowpea landraces, including the "stay green" phenotype (Muchero et al, 2009) (Muchero et al, 2010). Similar quantitative loci were also identified in asparagus bean (Xu et al, 2015). Whole plant physiology mechanisms therefore contribute to plant droughtstress adaptation.…”

“…Studying 40 cowpea genotypes, Belko et al (2013) found that drought-sensitive genotypes had higher transpiration rates than drought-tolerant genotypes both in well-watered and vapour pressure deficit conditions (Belko et al, 2013). Natural variation in drought resistance in a related species, Vigna unguiculata sesquipedalis (asparagus bean), was also attributed to variation in transpiration rates in response to vapour pressure deficit and soil drought (Xu et al, 2015). An explanation for our results could be that transpiration physiology and other mechanisms might contribute to local adaptation.…”

Genomic regions, cellular components and gene regulatory basis underlying pod length variations in cowpea (V. unguiculata L. Walp)

“…A custom Agilent microarray targeting 29 471 cowpea unigenes was transferred from a previous Roche NimbleGen cowpea microarray (Xu et al, 2015). Hybridizations were performed for long-pod pools and short-pod pools, each consisting of RNA from seven independent genotypes, in three replicates.…”

“…Details of the 14 genotypes used for pooling can be found in Table S1. Methods for RNA extraction, purification and quantification were as described in Xu et al (2015). All cDNA were labelled with the fluorescent dye Cy5-dCTP using cRNA amplification and labelling kit (CapitalBio, Beijing, China).…”