Expressions of OsHKT1, OsHKT2, and OsVHA are differentially regulated under NaCl stress in salt-sensitive and salt-tolerant rice (Oryza sativa L.) cultivars

Abstract

Under NaCl-dominated salt stress, the key to plant survival is maintaining a low cytosolic Na(+) level or Na(+)/K(+) ratio. The OsHKT1, OsHKT2, and OsVHA transporter genes might play important roles in maintaining cytosolic Na(+) homeostasis in rice (Oryza sativa L. indica cvs Pokkali and BRRI Dhan29). Upon NaCl stress, the OsHKT1 transcript was significantly down-regulated in salt-tolerant cv. Pokkali, but not in salt-sensitive cv. BRRI Dhan29. NaCl stress induced the expression of OsHKT2 and OsVHA in both Pokkali and BRRI Dhan29. In cv. Pokkali, OsHKT2 and OsVHA transcripts were induced immediately after NaCl stress. However, in cv. BRRI Dhan29, the induction of OsHKT2 was quite low and of OsVHA was low and delayed, compared with that in cv. Pokkali. OsHKT2 and OsVHA induction mostly occurred in the phloem, in the transition from phloem to mesophyll cells, and in the mesophyll cells of the leaves. The vacuolar area in cv. Pokkali did not change under either short- (5-10 min) or long-term (24 h) salt stress, although it significantly increased 24 h after the stress in cv. BRRI Dhan29. When expressional constructs of VHA-c and VHA-a with YFP and CFP were introduced into isolated protoplasts of cvs Pokkali and BRRI Dhan29, the fluorescence resonance energy transfer (FRET) efficiency between VHA-c and VHA-a upon salt stress decreased slightly in cv. Pokkali, but increased significantly in cv. BRRI Dhan29. The results suggest that the salt-tolerant cv. Pokkali regulates the expression of OsHKT1, OsHKT2, and OsVHA differently from how the salt-sensitive cv. BRRI Dhan29 does. Together, these proteins might confer salt tolerance in Pokkali by maintaining a low cytosolic Na(+) level and a correct ratio of cytosolic Na(+)/K(+).

Diversity in Expression Patterns and Functional Properties in the Rice HKT Transporter Family

“…The tissue specificity of OsHKT2;1 expression presented in this study on the japonica rice 'Nipponbare' is consistent with the pattern previously reported in the same cultivar by Horie et al (2007) and overlaps with, but also differs slightly from, the expression patterns reported in indica rice varieties (Golldack et al, 2002;Kader et al, 2006). Our study also provides the first information on two other HKT transporters, OsHKT1;1 and OsHKT1;3.…”

“…Information on tissue localization was available for three members of each HKT subfamily so far: AtHKT1;1 from Arabidopsis (Berthomieu et al, 2003;Sunarpi et al, 2005), OsHKT1;5 from rice (Ren et al, 2005), and McHKT1;1 from ice plant (Mesembryanthemum crystallinum; Su et al, 2003) for subfamily 1; TaHKT2;1 from wheat (Schachtman and Schroeder, 1994), OsHKT2;1 (Golldack et al, 2002;Kader et al, 2006;Horie et al, 2007), and OsHKT2;2 (Kader et al, 2006) from rice for subfamily 2. The whole set of data emphasized that HKT transporters are strongly expressed in tissues (root epidermis and cortex, xylem and phloem, vascular bundle regions) playing crucial roles in ion uptake or long-distance transport and redistribution in the plant.…”

A Single Amino-Acid Substitution in the Sodium Transporter HKT1 Associated with Plant Salt Tolerance

“…Excess of Na + in the cytosol counteracts the optimal cytosolic Na + /K + ratio, and is recognized as K + deficiency. Inducing HKT1 under such K + deficiency conditions seems detrimental if the HKT1 protein were to be Na + -specific (Kader et al, 2006). Under salt stress, when cytosolic Na + concentration reaches a toxic level, plants activate highaffinity K + transporters for K + uptake that adjust cellular Na + /K + balance (Yao et al, 2010;Wang et al, 2014).…”

Molecular characterization and function analysis of the rice OsDUF946 family

“…LEA proteins are mainly low-molecular-weight (10-30 kDa) proteins involved in protecting higher plants from damage caused by environmental stresses, especially drought or dehydration [42][43][44][45]. HKT transporters mediate Na C unloading from the xylem under salinity stress, which prevents Na C overaccumulation in leaves, thereby protecting photosynthetic organs [46][47][48][49]. It is, therefore, tempting to speculate that the overexpression of OsDUF946.4 might have resulted in upregulated expression of LEA protein-like and HKT-transporter-like genes in E. coli, which could have led to the enhanced tolerance to drought and salinity.…”