OsHKT1;4-mediated Na+ transport in stems contributes to Na+ exclusion from leaf blades of rice at the reproductive growth stage upon salt stress

Kei Suzuki, Naoki Yamaji, Alex Costa, Eiji Okuma, Natsuko I. Kobayashi, Tatsuhiko Kashiwagi, Maki Katsuhara, Cun Wang, Keitaro Tanoi, Yoshiyuki Murata, Julian I. Schroeder, Jian Feng Ma, Tomoaki Horie

Research output: Contribution to journalArticle

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Abstract

Background: Na+ exclusion from leaf blades is one of the key mechanisms for glycophytes to cope with salinity stress. Certain class I transporters of the high-affinity K+ transporter (HKT) family have been demonstrated to mediate leaf blade-Na+ exclusion upon salinity stress via Na+-selective transport. Multiple HKT1 transporters are known to function in rice (Oryza sativa). However, the ion transport function of OsHKT1;4 and its contribution to the Na+ exclusion mechanism in rice remain to be elucidated. Results: Here, we report results of the functional characterization of the OsHKT1;4 transporter in rice. OsHKT1;4 mediated robust Na+ transport in Saccharomyces cerevisiae and Xenopus laevis oocytes. Electrophysiological experiments demonstrated that OsHKT1;4 shows strong Na+ selectivity among cations tested, including Li+, Na+, K+, Rb+, Cs+, and NH4 +, in oocytes. A chimeric protein, EGFP-OsHKT1;4, was found to be functional in oocytes and targeted to the plasma membrane of rice protoplasts. The level of OsHKT1;4 transcripts was prominent in leaf sheaths throughout the growth stages. Unexpectedly however, we demonstrate here accumulation of OsHKT1;4 transcripts in the stem including internode II and peduncle in the reproductive growth stage. Moreover, phenotypic analysis of OsHKT1;4 RNAi plants in the vegetative growth stage revealed no profound influence on the growth and ion accumulation in comparison with WT plants upon salinity stress. However, imposition of salinity stress on the RNAi plants in the reproductive growth stage caused significant Na+ overaccumulation in aerial organs, in particular, leaf blades and sheaths. In addition, 22Na+ tracer experiments using peduncles of RNAi and WT plants suggested xylem Na+ unloading by OsHKT1;4. Conclusions: Taken together, our results indicate a newly recognized function of OsHKT1;4 in Na+ exclusion in stems together with leaf sheaths, thus excluding Na+ from leaf blades of a japonica rice cultivar in the reproductive growth stage, but the contribution is low when the plants are in the vegetative growth stage.

Original languageEnglish
Article number22
JournalBMC Plant Biology
Volume16
Issue number1
DOIs
Publication statusPublished - Jan 19 2016

Fingerprint

leaf blade
salt stress
developmental stages
rice
stems
transporters
oocytes
peduncle
vegetative growth
recombinant fusion proteins
Xenopus laevis
ion transport
internodes
protoplasts
xylem
tracer techniques
leaves
Saccharomyces cerevisiae
cations
Oryza sativa

Keywords

  • HKT
  • Na transport
  • Rice
  • Salinity stress

ASJC Scopus subject areas

  • Plant Science

Cite this

OsHKT1;4-mediated Na+ transport in stems contributes to Na+ exclusion from leaf blades of rice at the reproductive growth stage upon salt stress. / Suzuki, Kei; Yamaji, Naoki; Costa, Alex; Okuma, Eiji; Kobayashi, Natsuko I.; Kashiwagi, Tatsuhiko; Katsuhara, Maki; Wang, Cun; Tanoi, Keitaro; Murata, Yoshiyuki; Schroeder, Julian I.; Ma, Jian Feng; Horie, Tomoaki.

In: BMC Plant Biology, Vol. 16, No. 1, 22, 19.01.2016.

Research output: Contribution to journalArticle

Suzuki, Kei ; Yamaji, Naoki ; Costa, Alex ; Okuma, Eiji ; Kobayashi, Natsuko I. ; Kashiwagi, Tatsuhiko ; Katsuhara, Maki ; Wang, Cun ; Tanoi, Keitaro ; Murata, Yoshiyuki ; Schroeder, Julian I. ; Ma, Jian Feng ; Horie, Tomoaki. / OsHKT1;4-mediated Na+ transport in stems contributes to Na+ exclusion from leaf blades of rice at the reproductive growth stage upon salt stress. In: BMC Plant Biology. 2016 ; Vol. 16, No. 1.
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abstract = "Background: Na+ exclusion from leaf blades is one of the key mechanisms for glycophytes to cope with salinity stress. Certain class I transporters of the high-affinity K+ transporter (HKT) family have been demonstrated to mediate leaf blade-Na+ exclusion upon salinity stress via Na+-selective transport. Multiple HKT1 transporters are known to function in rice (Oryza sativa). However, the ion transport function of OsHKT1;4 and its contribution to the Na+ exclusion mechanism in rice remain to be elucidated. Results: Here, we report results of the functional characterization of the OsHKT1;4 transporter in rice. OsHKT1;4 mediated robust Na+ transport in Saccharomyces cerevisiae and Xenopus laevis oocytes. Electrophysiological experiments demonstrated that OsHKT1;4 shows strong Na+ selectivity among cations tested, including Li+, Na+, K+, Rb+, Cs+, and NH4 +, in oocytes. A chimeric protein, EGFP-OsHKT1;4, was found to be functional in oocytes and targeted to the plasma membrane of rice protoplasts. The level of OsHKT1;4 transcripts was prominent in leaf sheaths throughout the growth stages. Unexpectedly however, we demonstrate here accumulation of OsHKT1;4 transcripts in the stem including internode II and peduncle in the reproductive growth stage. Moreover, phenotypic analysis of OsHKT1;4 RNAi plants in the vegetative growth stage revealed no profound influence on the growth and ion accumulation in comparison with WT plants upon salinity stress. However, imposition of salinity stress on the RNAi plants in the reproductive growth stage caused significant Na+ overaccumulation in aerial organs, in particular, leaf blades and sheaths. In addition, 22Na+ tracer experiments using peduncles of RNAi and WT plants suggested xylem Na+ unloading by OsHKT1;4. Conclusions: Taken together, our results indicate a newly recognized function of OsHKT1;4 in Na+ exclusion in stems together with leaf sheaths, thus excluding Na+ from leaf blades of a japonica rice cultivar in the reproductive growth stage, but the contribution is low when the plants are in the vegetative growth stage.",
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AU - Suzuki, Kei

AU - Yamaji, Naoki

AU - Costa, Alex

AU - Okuma, Eiji

AU - Kobayashi, Natsuko I.

AU - Kashiwagi, Tatsuhiko

AU - Katsuhara, Maki

AU - Wang, Cun

AU - Tanoi, Keitaro

AU - Murata, Yoshiyuki

AU - Schroeder, Julian I.

AU - Ma, Jian Feng

AU - Horie, Tomoaki

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N2 - Background: Na+ exclusion from leaf blades is one of the key mechanisms for glycophytes to cope with salinity stress. Certain class I transporters of the high-affinity K+ transporter (HKT) family have been demonstrated to mediate leaf blade-Na+ exclusion upon salinity stress via Na+-selective transport. Multiple HKT1 transporters are known to function in rice (Oryza sativa). However, the ion transport function of OsHKT1;4 and its contribution to the Na+ exclusion mechanism in rice remain to be elucidated. Results: Here, we report results of the functional characterization of the OsHKT1;4 transporter in rice. OsHKT1;4 mediated robust Na+ transport in Saccharomyces cerevisiae and Xenopus laevis oocytes. Electrophysiological experiments demonstrated that OsHKT1;4 shows strong Na+ selectivity among cations tested, including Li+, Na+, K+, Rb+, Cs+, and NH4 +, in oocytes. A chimeric protein, EGFP-OsHKT1;4, was found to be functional in oocytes and targeted to the plasma membrane of rice protoplasts. The level of OsHKT1;4 transcripts was prominent in leaf sheaths throughout the growth stages. Unexpectedly however, we demonstrate here accumulation of OsHKT1;4 transcripts in the stem including internode II and peduncle in the reproductive growth stage. Moreover, phenotypic analysis of OsHKT1;4 RNAi plants in the vegetative growth stage revealed no profound influence on the growth and ion accumulation in comparison with WT plants upon salinity stress. However, imposition of salinity stress on the RNAi plants in the reproductive growth stage caused significant Na+ overaccumulation in aerial organs, in particular, leaf blades and sheaths. In addition, 22Na+ tracer experiments using peduncles of RNAi and WT plants suggested xylem Na+ unloading by OsHKT1;4. Conclusions: Taken together, our results indicate a newly recognized function of OsHKT1;4 in Na+ exclusion in stems together with leaf sheaths, thus excluding Na+ from leaf blades of a japonica rice cultivar in the reproductive growth stage, but the contribution is low when the plants are in the vegetative growth stage.

AB - Background: Na+ exclusion from leaf blades is one of the key mechanisms for glycophytes to cope with salinity stress. Certain class I transporters of the high-affinity K+ transporter (HKT) family have been demonstrated to mediate leaf blade-Na+ exclusion upon salinity stress via Na+-selective transport. Multiple HKT1 transporters are known to function in rice (Oryza sativa). However, the ion transport function of OsHKT1;4 and its contribution to the Na+ exclusion mechanism in rice remain to be elucidated. Results: Here, we report results of the functional characterization of the OsHKT1;4 transporter in rice. OsHKT1;4 mediated robust Na+ transport in Saccharomyces cerevisiae and Xenopus laevis oocytes. Electrophysiological experiments demonstrated that OsHKT1;4 shows strong Na+ selectivity among cations tested, including Li+, Na+, K+, Rb+, Cs+, and NH4 +, in oocytes. A chimeric protein, EGFP-OsHKT1;4, was found to be functional in oocytes and targeted to the plasma membrane of rice protoplasts. The level of OsHKT1;4 transcripts was prominent in leaf sheaths throughout the growth stages. Unexpectedly however, we demonstrate here accumulation of OsHKT1;4 transcripts in the stem including internode II and peduncle in the reproductive growth stage. Moreover, phenotypic analysis of OsHKT1;4 RNAi plants in the vegetative growth stage revealed no profound influence on the growth and ion accumulation in comparison with WT plants upon salinity stress. However, imposition of salinity stress on the RNAi plants in the reproductive growth stage caused significant Na+ overaccumulation in aerial organs, in particular, leaf blades and sheaths. In addition, 22Na+ tracer experiments using peduncles of RNAi and WT plants suggested xylem Na+ unloading by OsHKT1;4. Conclusions: Taken together, our results indicate a newly recognized function of OsHKT1;4 in Na+ exclusion in stems together with leaf sheaths, thus excluding Na+ from leaf blades of a japonica rice cultivar in the reproductive growth stage, but the contribution is low when the plants are in the vegetative growth stage.

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