Common bean SNP alleles and candidate genes affecting photosynthesis under contrasting water regimes

Water deficit is a major worldwide constraint to common bean(Phaseolus vulgaris L.)production,being photosynthesis one of the most affected physiological processes.To gain insights into the genetic basis of the photosynthetic response of common bean under water-limited conditions,a collection of 158 Portuguese accessions was grown under both well-watered and water-deficit regimes.Leaf gas-exchange parameters were measured and photosynthetic pigments quantified.The same collection was genotyped using SNP arrays,and SNP-trait associations tested considering a linear mixed model accounting for the genetic relatedness among accessions.A total of 133 SNP-trait associations were identified for net CO 2 assimilation rate,transpiration rate,stomatal conductance,and chlorophylls a and b,carotenes,and xanthophyll contents.Ninety of these associations were detected under water-deficit and 43 under well-watered conditions,with only two associations common to both treatments.Identified candidate genes revealed that stomatal regulation,protein translocation across membranes,redox mechanisms,hormone,and osmotic stress signaling were the most relevant processes involved in common bean response to water-limited conditions.These candidates are now preferential targets for common bean water-deficit-tolerance breeding.Additionally,new sources of water-deficit tolerance of Andean,Mesoamerican,and admixed origin were detected as accessions valuable for breeding,and not yet explored.

Shared and tailored common bean transcriptomic responses to combined fusarium wilt and water deficit

Common bean(Phaseolus vulgaris L.),one of the most consumed food legumes worldwide,is threatened by two main constraints that are found frequently together in nature,water deficit(WD)and fusarium wilt(Fop).To understand the shared and unique responses of common bean to Fop and WD,we analyzed the transcriptomic changes and phenotypic responses in two accessions,one resistant and one susceptible to both stresses,exposed to single and combined stresses.Physiological responses(photosynthetic performance and pigments quantification)and disease progression were also assessed.The combined FopWD imposition negatively affected the photosynthetic performance and increased the susceptible accession disease symptoms.The susceptible accession revealed a higher level of transcriptional changes than the resistant one,and WD single stress triggered the highest transcriptional changes.While 89 differentially expressed genes were identified exclusively in combined stresses for the susceptible accession,35 were identified in the resistant one.These genes belong mainly to“stress”,“signaling”,“cell wall”,“hormone metabolism”,and“secondary metabolism”functional categories.Among the up-regulated genes with higher expression in the resistant accession,the cysteine-rich secretory,antigen 5 and Pr-1(CAP)superfamily protein,a ribulose bisphosphate carboxylase family protein,and a chitinase A seem promising targets for multiple stress breeding.

First genetic linkage map of Lathyrus cicera based on RNA sequencing-derived markers: Key tool for genetic mapping of disease resistance

The Lathyrus cicera transcriptome was analysed in response to rust(Uromyces pisi)infection to develop novel molecular breeding tools with potential for genetic mapping of resistance in this robust orphan legume species.One RNA-seq library each was generated from control and rust-inoculated leaves from two L.cicera genotypes with contrasting quantitative resistance,de novo assembled into contigs and sequence polymorphisms were identified.In toto,19,224 SNPs differentiate the susceptible from the partially resistant genotype’s transcriptome.In addition,we developed and tested 341 expressed E-SSR markers from the contigs,of which 60.7%varied between the two L.cicera genotypes.A first L.cicera linkage map was created using part of the developed markers in a RIL population from the cross of the two genotypes.This map contains 307 markers,covered 724.2 cM and is organised in 7 major and 2 minor linkage groups,with an average mapping interval of 2.4 cM.The genic markers also enabled us to compare their position in L.cicera map with the physical position of the same markers mapped on Medicago truncatula genome,highlighting a high macrosyntenic conservation between both species.This study provides a large new set of genic polymorphic molecular markers with potential for mapping rust resistances.It represents the first step towards genomics-assisted precision breeding in L.cicera.

Performance index: An expeditious tool to screen for improved drought resistance in the Lathyrus genus

Some species of the Lathyrus genus are among the most promising crops for marginal lands, with high resilience to drought, flood, and fungal diseases, combined with high yields and seed nutritional value. However, lack of knowledge on the mechanisms underlying its outstanding performance and methodologies to identify elite genotypes has hampered its proper use in breeding. Chlorophyl a fast fluorescence transient （JIP test）, was used to evaluate water deficit （WD） resistance in Lathyrus genus. Our results reveal unaltered photochemical values for al studied genotypes showing resistance to mild WD. Under severe WD, two Lathyrus sativus genotypes showed remarkable resilience maintaining the photochemical efficiency, contrary to other genotypes studied. Performance index （PIABS） is the best parameter to screen genotypes with improved performance and grain production under WD. Moreover, we found that JIP indices are good indicators of genotypic grain production under WD. Quantum yield of electron transport （wEo） and efficiency with which＆trapped excitons can move electrons further than QA （c0） revealed as important traits related to improved photosyn-thetic performance and should be exploited in future Lathyrus germplasm improvements. The JIP test herein described showed to be an expeditious tool to screen and to identify elite genotypes with improved drought resistance.