Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
, 13, 32

Salinity Tolerance, Na+ Exclusion and Allele Mining of HKT1;5 in Oryza Sativa and O. Glaberrima: Many Sources, Many Genes, One Mechanism?

Affiliations

Salinity Tolerance, Na+ Exclusion and Allele Mining of HKT1;5 in Oryza Sativa and O. Glaberrima: Many Sources, Many Genes, One Mechanism?

John Damien Platten et al. BMC Plant Biol.

Abstract

Background: Cultivated rice species (Oryza sativa L. and O. glaberrima Steud.) are generally considered among the crop species most sensitive to salt stress. A handful of lines are known to be tolerant, and a small number of these have been used extensively as donors in breeding programs. However, these donors use many of the same genes and physiological mechanisms to confer tolerance. Little information is available on the diversity of mechanisms used by these species to cope with salt stress, and there is a strong need to identify varieties displaying additional physiological and/or genetic mechanisms to confer higher tolerance.

Results: Here we present data on 103 accessions from O. sativa and 12 accessions from O. glaberrima, many of which are identified as salt tolerant for the first time, showing moderate to high tolerance of high salinity. The correlation of salinity-induced senescence (as judged by the Standard Evaluation System for Rice, or SES, score) with whole-plant and leaf blade Na+ concentrations was high across nearly all accessions, and was almost identical in both O. sativa and O. glaberrima. The association of leaf Na+ concentrations with cultivar-groups was very weak, but association with the OsHKT1;5 allele was generally strong. Seven major and three minor alleles of OsHKT1;5 were identified, and their comparisons with the leaf Na+ concentration showed that the Aromatic allele conferred the highest exclusion and the Japonica allele the least. A number of exceptions to this association with the Oryza HKT1;5 allele were identified; these probably indicate the existence of additional highly effective exclusion mechanisms. In addition, two landraces were identified, one from Thailand and the other from Senegal, that show high tissue tolerance.

Conclusions: Significant variation in salinity tolerance exists within both cultivated Oryza species, and this is the first report of significant tolerance in O. glaberrima. The majority of accessions display a strong quantitative relationship between tolerance and leaf blade Na+ concentration, and thus the major tolerance mechanisms found in these species are those contributing to limiting sodium uptake and accumulation in active leaves. However, there appears to be genetic variation for several mechanisms that affect leaf Na+ concentration, and rare cases of accessions displaying different mechanisms also occur. These mechanisms show great promise for improving salt tolerance in rice over that available from current donors.

Figures

Figure 1
Figure 1
Geographic provenance of tolerant landraces. Geographic provenance of tolerant landraces identified in the literature or through this study, and association with HKT1;5 allele.
Figure 2
Figure 2
Tolerant landraces stem from all cultivar-groups of O. sativa. SNP genotyping on the 384-plex indica-indica Illumina set [46]. The majority of tolerant lines identified fall within the indica cultivar-group, but a large number originate from the aromatic cultivar-group, and other cultivar-groups are also represented. Additional lines found to be tolerant and known to be in particular cultivar-groups are listed by the indicated clades.
Figure 3
Figure 3
Salinity-induced injury is highly correlated with leaf Na+ concentrations across the entire species. (A). The visual SES injury score was highly correlated with leaf Na+ concentration across all cultivar-groups of O. sativa, and in all tested accessions of O. glaberrima. The linear regression line is shown, together with ± SE intervals. However, no such relationship was seen with leaf K+ concentration (B) or root Na+ concentration (C). Likewise, there was no relationship between leaf Na+ and K+ concentrations (D ratio/FL478, mmol.gDW-1 data). Similar relationships were seen in both the youngest and second-youngest expanded leaf (at time of salinisation; L5 and L6 in these data, and the only leaves still photosynthetically active; leaf 6 data not shown). FL478 was used as the tolerant check.
Figure 4
Figure 4
Tolerance is not well correlated with cultivar-groups. Tolerance is not well correlated with cultivar-groups in O. sativa, though few japonica accessions score tolerant overall, and few aromatic accessions score sensitive. Members of the aus cultivar-group generally score moderate to highly tolerant; indica accessions show a wide variability. Few accessions of O. glaberrima have been screened, but these seem to show as wide a range of tolerance and Na+ exclusion as seen in O. sativa.
Figure 5
Figure 5
Allele mining of HKT1;5 from O. sativa and O. glaberrima. Sequencing and phylogeny of HKT1;5 from O. sativa and O. glaberrima. A. Regions amplified and sequenced. These total approximately 6.5 kb, including the full coding region and approximately 3.5 kb of promoter. Exons of the OsHKT1;5 gene are shown as filled, linked arrows, primers/PCR products by linked green and red arrows. B. Minimum-evolution tree of sequenced regions, based on the number of differences (10,000 bootstrap replicates, pairwise deletion of gaps). Selected lines possessing each allele are indicated. Yellow shading indicates high tolerance and high Na+ exclusion, and green indicates moderate tolerance and exclusion. Blue shading indicates sensitivity and low Na+ exclusion. The Daw allele lines (unshaded) are tolerant/highly tolerant but do not show the same amount of Na+ exclusion. Other unshaded lines have not been tested for salinity tolerance or leaf Na+ concentrations.
Figure 6
Figure 6
Na+ concentration in the leaf is highly associated with the HKT1;5 allele across diverse accessions. Association of Na+ concentrations in leaves with the HKT1;5 allele. Mean (solid horizontal line) and SE (broken horizontal lines) for each allele group are indicated. Lines carrying the Aromatic allele generally showed the greatest exclusion, followed by the Aus and Hasawi alleles. Lines carrying the Japonica allele generally showed the least exclusion, followed by lines with the IR29 allele.
Figure 7
Figure 7
Na+ concentration in tolerant O. glaberrima accessions. Na+ concentrations in tolerant O. glaberrima accessions; CG14 is included as a sensitive check. Lines 351, 357 and 358 all showed exclusion equivalent to or better than FL478, the tolerant check; in the case of 357, it was below reliable detection limits in leaf 6.
Figure 8
Figure 8
Na+ concentrations in selected accessions from Iran. Na+ concentrations in various organs of selected accessions from Iran and checks. Note that while FL478 (tolerant check) has lower concentrations in its leaf blade and sheath than a sensitive line such as Nipponbare, it actually contains an increased concentration in roots. This is typical of many tolerant Na+-excluding lines, but the relationship is broken in these lines from Iran (Larome, Massan Mulat, Mulai); which contain low Na+ concentrations in roots in addition to aerial portions.
Figure 9
Figure 9
Genetic separability of tolerance mechanisms. Further evidence that different lines may have different genes conferring tolerance. SES scores of an F2 population derived from the cross of the two tolerant genotypes FL478 × Hasawi were recorded after treatment with 150 mM NaCl (applied at 21 days after germination). The F2 population displayed transgressive segregation in both the sensitive (early timepoint, 14 days after salinisation, das; A) and tolerant (late timepoint, 34 days after salinisation; B) directions, compared with FL478 and Hasawi controls. IR29 (sensitive) is included for comparison.

Similar articles

See all similar articles

Cited by 43 articles

See all "Cited by" articles

References

    1. Ismail A, Thomson M, Singh R, Gregorio G, Mackill D. Designing rice varieties adapted to coastal areas of South and Southeast Asia. Journal of the Indian Society for Coastal Agricultural Research. 2008;26:69–73.
    1. Ismail A, Tuong T. In: Natural resource management for poverty reduction and environmental sustainability in rice-based systems. Haefele S, Ismail A, editor. Los Banos, Philippines: International Rice Research Institute; 2009. Brackish water coastal zones of the monsoon tropics: challenges and opportunities; pp. 113–121.
    1. Wassmann R, Jagadish SVK, Heuer S, Ismail A, Redoña E, Serraj R, Singh RK, Howell G, Pathak H, Sumfleth K. Climate change affecting rice production: the physiological and agronomic basis for possible adaptation strategies. Adv Agron. 2009;101:59–122.
    1. Akbar M, Yabuno T, Nakao S. Breeding for saline-resistant varieties of rice I. Variability for salt tolerance among some rice varieties. Japanese Journal of Breeding. 1972;22(5):277–284.
    1. Ismail A, Heuer S, Thomson M, Wissuwa M. Genetic and genomic approaches to develop rice germplasm for problem soils. Plant Mol Biol. 2007;65(4):547–570. doi: 10.1007/s11103-007-9215-2. http://dx.doi.org/10.1007/s11103-007-9215-2. - DOI - DOI - PubMed

Publication types

Feedback