A retrotransposon in an HKT1 family sodium transporter causes variation of leaf Na⁺ exclusion and salt tolerance in maize

Abstract

Soil salinity is one of several major abiotic stresses that constrain maize productivity worldwide. An improved understanding of salt-tolerance mechanisms will thus enhance the breeding of salt-tolerant maize and boost productivity. Previous studies have indicated that the maintenance of leaf Na concentration is essential for maize salt tolerance, and the difference in leaf Na exclusion has previously been associated with variation in salt tolerance between maize varieties. Here, we report the identification and functional characterization of a maize salt-tolerance quantitative trait locus (QTL), Zea mays Na Content1 (ZmNC1), which encodes an HKT-type transporter (designated as ZmHKT1). We show that a natural ZmHKT1 loss-of-function allele containing a retrotransposon insertion confers increased accumulation of Na in leaves, and salt hypersensitivity. We next show that ZmHKT1 encodes a plasma membrane-localized Na -selective transporter, and is preferentially expressed in root stele (including the parenchyma cells surrounding the xylem vessels). We also show that loss of ZmHKT1 function increases xylem sap Na concentration and causes increased root-to-shoot Na delivery, indicating that ZmHKT1 promotes leaf Na exclusion and salt tolerance by withdrawing Na from the xylem sap. We conclude that ZmHKT1 is a major salt-tolerance QTL and identifies an important new gene target in breeding for improved maize salt tolerance.

A Grain of Salt

“…Common SNPs between the 50k and 9K iSelect platforms 22 aligned this association with a region recently shown to contain HvHKT1;5 20, 23 , and in the barley genome sequence HORVU4Hr1G087960, 140kb from the top scoring SNP (chr4H_638774955), was annotated as a homolog of OsHKT1;5. Considering this and previous functional studies 24–27 we conclude that HORVU4Hr1G087960 is the Na + specific transporter HvHKT1;5 .…”

Systematic hormone-metabolite network provides insights of high salinity tolerance inPongamia pinnata(L.) pierre

“…In this study,expression of HKT1:1 followed similar trend in both leaves and roots of salt stressed plants. Previous studies suggested that HKT family transporter proteins can mediate exclusion of Na + from leaves and roots by translocating shoot-to-rootand root-to-shoot Na + delivery by withdrwaing Na + from xylem stream into phloem (Munns et al, 2012; Hill et al, 2013; An et al, 2017; Zhang et al, 2018). Induction of HKT1:1 expression upon initial imposition of salt stress in both leaves and roots may promote Na + exclusion tolimit Na + toxcity in the respective tissues(Zhang et al, 2018).…”

“…Previous studies suggested that HKT family transporter proteins can mediate exclusion of Na + from leaves and roots by translocating shoot-to-rootand root-to-shoot Na + delivery by withdrwaing Na + from xylem stream into phloem (Munns et al, 2012; Hill et al, 2013; An et al, 2017; Zhang et al, 2018). Induction of HKT1:1 expression upon initial imposition of salt stress in both leaves and roots may promote Na + exclusion tolimit Na + toxcity in the respective tissues(Zhang et al, 2018). However, with increasing salt stress treatment time, the marginal expression of HKT1:1genemay regulate the retrevial of Na + from the xylem (Davenport et al, 2007; Ali et al, 2016).…”

The full-length transcriptome of Spartina alterniflora reveals the complexity of high salt tolerance in monocotyledonous halophyte

“…These results suggest that the long-distance transport of Na + from root to leave may continue to be active under high salt stress in Spartina . One of the explanations is that leaves of Spartina have salt glands (Nestler, 1977; Subudhi & Baisakh, 2011) and can secrete salt, so that high expression of SaHKT1 may not be required to shut down Na + transport compared to other plants (Jaime-Perez et al, 2017; M. Zhang et al, 2018).…”