Abstract
Durum wheat (Triticum turgidum subsp. durum) is more salt sensitive than bread wheat (Triticum aestivum). A novel source of Na(+) exclusion conferring salt tolerance to durum wheat is present in the durum wheat Line 149 derived from Triticum monococcum C68-101, and a quantitative trait locus contributing to low Na(+) concentration in leaf blades, Nax1, mapped to chromosome 2AL. In this study, we used the rice (Oryza sativa) genome sequence and data from the wheat expressed sequence tag deletion bin mapping project to identify markers and construct a high-resolution map of the Nax1 region. Genes on wheat chromosome 2AL and rice chromosome 4L had good overall colinearity, but there was an inversion of a chromosomal segment that includes the Nax1 locus. Two putative sodium transporter genes (TmHKT7) related to OsHKT7 were mapped to chromosome 2AL. One TmHKT7 member (TmHKT7-A1) was polymorphic between the salt-tolerant and -sensitive lines, and cosegregated with Nax1 in the high-resolution mapping family. The other TmHKT7 member (TmHKT7-A2) was located within the same bacterial artificial chromosome contig of approximately 145 kb as TmHKT7-A1. TmHKT7-A1 and -A2 showed 83% amino acid identity. TmHKT7-A2, but not TmHKT7-A1, was expressed in roots and leaf sheaths of the salt-tolerant durum wheat Line 149. The expression pattern of TmHKT7-A2 was consistent with the physiological role of Nax1 in reducing Na(+) concentration in leaf blades by retaining Na(+) in the sheaths. TmHKT7-A2 could control Na(+) unloading from xylem in roots and sheaths.
Highlights
Durum wheat (Triticum turgidum subsp. durum) is more salt sensitive than bread wheat (Triticum aestivum)
We provide evidence that a putative sodium transporter is a candidate gene for Nax1, which may control Na1 unloading from xylem in roots and sheaths as indicated by its expression pattern and physiological role of Na1 partitioning into leaf sheaths
Seventy-four wheat expressed sequence tags (wESTs) had been mapped into the same physical region that had significant DNA sequence homology to rice genes in the syntenic region of 17.8 to 34.4 Mb on rice chromosome 4L
Summary
Durum wheat (Triticum turgidum subsp. durum) is more salt sensitive than bread wheat (Triticum aestivum). We used the rice (Oryza sativa) genome sequence and data from the wheat expressed sequence tag deletion bin mapping project to identify markers and construct a high-resolution map of the Nax region. TmHKT7-A2, but not TmHKT7-A1, was expressed in roots and leaf sheaths of the salt-tolerant durum wheat Line 149. The objective of this study was to use wESTs that were previously positioned in the physical deletion bins of wheat chromosome 2AL in conjunction with the rice genome sequence to define a detailed map position and clone a candidate gene for Nax. We provide evidence that a putative sodium transporter (closely related to OsHKT7) is a candidate gene for Nax, which may control Na1 unloading from xylem in roots and sheaths as indicated by its expression pattern and physiological role of Na1 partitioning into leaf sheaths
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