Legume-rhizobia symbiotic performance under abiotic stresses: factors influencing tolerance behaviour - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 129

2011, 2013; Mhadhbi et al., 2011a,c, 2013; Ahmad et al.,
2008, 2010, 2011, 2012, 2014; Ahmad, 2014).

enrich our understanding of successful symbiotic associ-
ations under stress.

8.7 Future prospects

references

Over the last decade, advances in sequencing tech-
nologies have brought an explosion of the available
genomic information regarding microbial as well as
plant genomes. Several genomes of microbial symbionts
of legumes, the genome sequences of the model legumes
Medicago truncatula and Lotus japonicus , as well as the
genome sequence of the most agronomically important
legume species, soybean ( Glycine max ), are now avail-
able. Gene expression analysis at the genomic level has
been made possible, and transcriptome profiling offers
valuable information about gene function under specific
conditions. Bioinformatics tools are also used for access
and analysis of the data (Li et al., 2011).
Comparative genomic analyses not only enable the
study of legume-specific gene families, but also provide a
framework to target phenotypes with specific character-
istics related to stress tolerance. Available methodolo gies
for next generation sequencing now allow the re-
sequencing of individuals with specific phenotypes so
that genomic information can be translated to gain a
deeper understanding of the genetic factors affecting
these phenotypes.
This strategy has already provided significant
information about the rhizobial partners. In bacteria
there are large differences in gene content even bet-
ween closely related strains, where a number of genes
conserved in all strains comprise the 'core' genes, and
genes that show variation between strains are 'accessory'
genes; this leads to the concept of the 'pangenome', that
is, the total number of genes detected not in individ-
uals or strains, but in the species as a whole. Symbiotic
diversity in Sinorhizobium meliloti has been studied by
comparative genomic analysis between different strains,
defining a set of accessory genes and regulons that may
contribute to the symbiotic process (Galardini et al.,
2011). Stress tolerance diversity may be analysed with a
similar approach in order to define genetic factors
related to tolerant phenotypes. Nevertheless, advances
in high-throughput sequencing may facilitate variant
discovery and genotyping, but linking genotypic vari-
ants to specific phenotypes is still a major task. Future
studies at the genomic and proteomic levels will further

Ahmad P (2014) Oxidative Damage to Plants: Antioxidant Networks
and Signaling . Academic Press, Elsevier.
Ahmad P, Sarwat M, Sharma S (2008) Reactive oxygen species,
antioxidants and signaling in plants. J Plant Biol 51:
167-173.
Ahmad P, Jaleel CA, Salem MA, Nabi G, Sharma S (2010) Roles
of enzymatic and non-enzymatic antioxidants in plants dur-
ing abiotic stress. Crit Rev Biotechnol 30: 161-175.
Ahmad P, Nabi G, Ashraf M (2011) Cadmium-induced oxida-
tive damage in mustard [ Brassica juncea (L.) Czern. & Coss.]
plants can be alleviated by salicylic acid. South Afr J Bot 77:
36-44.
Ahmad P, Hakeem KR, Kumar A, Ashraf M, Akram NA (2012)
Salt-induced changes in photosynthetic activity and oxidative
defense system of three cultivars of mustard ( Brassica juncea
L.) Afr J Biotechnol 11: 2694-2703.
Ahmad P, Ozturk M, Sharma S, Gucel S (2014) Effect of sodium
carbonate-induced salinity-alkalinity on some key osmopro-
tectants, protein profile, antioxidant enzymes, and lipid per-
oxidation in two mulberry ( Morus alba L.) cultivars. J Plant
Interactions 9: 460-467.
Aydi S, Drevon JJ, Abdelly C (2004) Effect of salinity on root-
nodule conductance to the oxygen diffusion in the Medicago
truncatula-Sinorhizobium meliloti symbiosis. Plant Physiol
Biochem 42: 833-840.
Bartoli CG, Casalongué CA, Simontacchi M, Marquez-Garcia B,
Foyer CH (2013) Interactions between hormone and redox
signalling pathways in the control of growth and cross toler-
ance to stress. Environ Exp Bot 94: 73-88.
Becana M, Dalton DA, Moran JF, Iturbe-Ormaetxe I, Matamoros
MA, Rubio MC (2000) Reactive oxygen species and antioxi-
dant in legume nodules. Physiol Plant 109: 372-381.
Becana M, Matamoros MA, Udvardi M, Dalton DA (2010)
Recent insights into antioxidant defenses of legume root
nodules. New Phytol 188: 960-976.
Ben Rhomdhane S, Tajini F, Trabelsi M, Aouani ME, Mhamdi R
(2007) Competition for nodule formation between intro-
duced strains of Mesorhizobium ciceri and native populations of
rhizobia nodulating chickpea ( Cicer arietinum ) in Tunisia.
World J. Microbiol Biotechnol 23: 1195-1201.
Chang C, Damiani I, Puppo A, Frendo P (2009) Redox changes
during the legume-rhizobium symbiosis. Mol Plant 2:
370-377.
Djébali N, Mhadhbi H, Lafitte C, Dumas B, Esquerré-Tugayé
MT, Aouani ME, Jacquet C (2011) Hydrogen peroxide scav-
enging mechanisms are components of Medicago truncatula
partial resistance to Aphanomyces euteiches . Eur J Plant Pathol
131: 559-571.