Heritable alteration in salt-tolerance in rice induced by introgression from wild rice (Zizania latifolia)

Abstract

Background: Introgression as a means of generating phenotypic novelty, including altered stress tolerance, is increasingly being recognized as common. The underlying basis for de novo genesis of phenotypic variation in the introgression lines remains largely unexplored. In this investigation, we used a rice line (RZ35) derived from introgressive hybridization between rice (Oryza sativa L.) and wild rice (Zizania latifolia Griseb.), along with its rice parental line (cv. Matsumae) as the experimental materials. We compared effects of salt stress on growth, ion homeostasis, and relevant gene expression between RZ35 and Matsumae, to explore possible mechanisms of heritable alteration in stress tolerance induced by the introgression.

Results: Contrary to our expectation, the results showed that the inhibitory effect of salt stress on growth of RZ35 was significantly greater than that of Matsumae. We further found that a major underlying cause for this outcome is that the introgression process weakened the capacity in Na+ exclusion under the salt stress condition, and hence, escalated the injuries of Na+ and Cl- in shoots of RZ35. Accordingly, based on q-RT-PCR analysis, four genes known to be involved in the Na+ exclusion, i.e., OsHKT1;5, OsSOS1, OsCIPK24 and OsCBL4, were found to be significantly down-regulated in roots of RZ35 relative to its rice parental line under the salt stress condition, thus implicating a gene expression regulation-based molecular mechanism underlying the difference in salt stress-tolerance between the introgression line and its rice parental line.

Conclusions: We show that introgression represents a potent means for rapidly generating de novo heritable variations in physiological traits like stress tolerance in plants, although the direction of the alteration appears unpredictable.

Figure 1

Effects of salt stress on growth in the introgression line RZ35 and its rice parental line, Matsumae . 14-day-old seedlings were subjected to salt stress (100 mM NaCl) for 5 d. The values shown are the means (± SE) of three biological replicates. Different letters above bars represent significantly different, according to least significant difference (LSD) test (P <0.05).

Figure 2

Effects of salt stress on survival rate, MDA (malondialdehyde) content and electrolyte leakage rate in the introgression line RZ35 and its rice parental line, Matsumae . 14-day-old seedlings were subjected to salt stress (100 mM NaCl). When the seedlings were subjected to salt stress for 5 d, the MDA content and electrolyte leakage rate of shoots were mensurated. When the seedlings were subjected to salt stress for 13 d, the survival rates were calculated. The values shown are the means (± SE) of three biological replicates. Different letters above bars represent significantly different, according to least significant difference (LSD) test (P <0.05).

Figure 3

Effects of salt stress on Na⁺, K⁺, Na⁺/K⁺and ST in the introgression line RZ35 and its rice parental line, Matsumae . The values shown are the means (± SE) of three biological replicates. Means followed by different letters among treatments at same time point are significantly different, according to least significant difference (LSD) test (P <0.05). 14-day-old seedlings were subjected to salt stress (100 mM NaCl) for 6 h, 24 h and 48 h. ST, selective transport capacity by different parts of plant for K⁺ over Na⁺. ST, selective transport capacity by different parts of plant for K⁺ over Na⁺. ST (root/shoot) = (Na⁺/K⁺ in root)/(Na⁺/K⁺ in shoot). The correlation analysis between ST and shoot Na⁺ content was performed (H).

Figure 4

Effects of salt stress on Cl^-contents in the introgression line RZ35 and its rice parental line, Matsumae . The values shown are the means (± SE) of three biological replicates. Means followed by different letters among treatments at same time point are significantly different, according to least significant difference (LSD) test (P <0.05). 14-day-old seedlings were subjected to salt stress (100 mM NaCl) for 6 h, 24 h and 48 h.

Figure 5

Effects of salt stress on the expression of OsSOS1 , OsCIPK24 and OsCBL4 in the introgression line RZ35 and its rice parental line, Matsumae . The values shown are the means (± SE) of three biological replicates. Means followed by different letters among treatments at same time point are significantly different, according to least significant difference (LSD) test (P <0.05). 14-day-old seedlings were subjected to salt stress (100 mM NaCl) for 6 h, 24 h and 48 h.

Figure 6

Effects of salt stress on the expression of OsNHX1 and OsNHX2 in the introgression line RZ35 and its rice parental line, Matsumae . The values shown are the means (± SE) of three biological replicates. Means followed by different letters among treatments at same time point are significantly different, according to least significant difference (LSD) test (P <0.05). 14-day-old seedlings were subjected to salt stress (100 mM NaCl) for 6 h, 24 h and 48 h.

Figure 7

Effects of salt stress on the expressions of OsHKT1;1 , OsHKT1;3 , OsHKT1;5 and OsHKT2;1 in rice- Z. latifolia introgressant ( RZ35 ) and its rice parental line ( Matsumae ). The values shown are the means (± SE) of three biological replicates. Means followed by different letters among treatments at same time point are significantly different, according to least significant difference (LSD) test ( P <0.05). 14-day-old seedlings were subjected to salt stress (100 mM NaCl) for 6 h, 24 h and 48 h.

Figure 8

Effects of salt stress on the expression of OsHAK family members and OsAKT1 in rice- Z. latifolia introgressant ( RZ35 ) and its rice parental line ( Matsumae ). The values shown are the means (± SE) of three biological replicates. Means followed by different letters among treatments at same time point are significantly different, according to least significant difference (LSD) test (P <0.05). 14-day-old seedlings were subjected to salt stress (100 mM NaCl) for 6 h, 24 h and 48 h.