Allelic variants of OsHKT1;1 underlie the divergence between indica and japonica subspecies of rice (Oryza sativa) for root sodium content.

Malachy T Campbell (1) , Nonoy Bandillo (1) , Fouad Al-Shiblawi (2, 2) , Sandeep Sharma (1) , Kan Liu (3, 1) , Qian Du (3, 1) , Aaron J Schmitz (1) , Chi Zhang (3, 1) , Anne-Aliénor Véry (2, 2) , Aaron J Lorenz (1) , Harkamal Walia (1)

1 University of Nebraska–Lincoln
2 BPMP - Biochimie et Physiologie Moléculaire des Plantes
3 School of Biological Sciences

Salinity is a major factor limiting crop productivity. Rice (Oryza sativa), a staple crop for the majority of the world, is highly sensitive to salinity stress. To discover novel sources of genetic variation for salt tolerance-related traits in rice, we screened 390 diverse accessions under 14 days of moderate (9 dS·m-1) salinity. In this study, shoot growth responses to moderate levels of salinity were independent of tissue Na+ content. A significant difference in root Na+ content was observed between the major subpopulations of rice, with indica accessions displaying higher root Na+ and japonica accessions exhibiting lower root Na+ content. The genetic basis of the observed variation in phenotypes was elucidated through genome-wide association (GWA). The strongest associations were identified for root Na+:K+ ratio and root Na+ content in a region spanning ~575 Kb on chromosome 4, named Root Na+ Content 4 (RNC4). Two Na+ transporters, HKT1;1 and HKT1;4 were identified as candidates for RNC4. Reduced expression of both HKT1;1 and HKT1;4 through RNA interference indicated that HKT1;1 regulates shoot and root Na+ content, and is likely the causal gene underlying RNC4. Three non-synonymous mutations within HKT1;1 were present at higher frequency in the indica subpopulation. When expressed in Xenopus oocytes the indica-predominant isoform exhibited higher inward (negative) currents and a less negative voltage threshold of inward rectifying current activation compared to the japonica-predominant isoform. The introduction of a 4.5kb fragment containing the HKT1;1 promoter and CDS from an indica variety into a japonica background, resulted in a phenotype similar to the indica subpopulation, with higher root Na+ and Na+:K+. This study provides evidence that HKT1;1 regulates root Na+ content, and underlies the divergence in root Na+ content between the two major subspecies in rice.

Mots clés: root; salt tolerance

Mots clés: canal à potassium; canal à sodium; racine; stress salin; tolérance au sel; transport d'ion; oryza sativa

Domaines: Biologie végétale

Malachy T Campbell, Nonoy Bandillo, Fouad Al-Shiblawi, Sandeep Sharma, Kan Liu, et al.. Allelic variants of OsHKT1;1 underlie the divergence between indica and japonica subspecies of rice (Oryza sativa) for root sodium content.. PLoS Genetics, 2017, 13 (6), pp.e1006823. ⟨10.1371/journal.pgen.1006823⟩. ⟨hal-01594512⟩