Comparative functional analyses of DWARF14 and KARRIKIN INSENSITIVE 2 in drought adaptation of Arabidopsis thaliana

Abstract

This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as

Negative Roles of Strigolactone-Related SMXL6, 7 and 8 Proteins in Drought Resistance in Arabidopsis

“…In the present study, by comparing drought resistance levels of various combinations of knock-out mutants of SMXL6, 7 and 8 genes, including single, double and triple mutants (Figure 1; Figure S1), we firmly showed that SMXL6, 7 and 8 are involved in regulating drought resistance in Arabidopsis plants as redundant negative regulators. Since SMXL6, 7 and 8 are repressors of the SL signaling [6,7], our results provide not only convincing proof for the functions of these three repressors but also an additional evidence to strengthen the positive role of SLs in regulating drought resistance in plants as reported earlier by numerous studies [16][17][18][19][20][21]. For instance, SL-depleted (e.g., max3 and max4) and SL-receptor (e.g., d14) Arabidopsis mutant plants, and SL-depleted L. japonicus (e.g., LjCCD7-silenced) and tomato (e.g., SlCCD7-silenced) transgenic plants were shown to exhibit susceptible phenotypes to various water-deficit stress conditions [16][17][18][19][20][21].…”

“…Thus, the increase in leaf surface temperatures of smxl6,7,8 mutant plants suggests that loss-of-functions of SMXL6, 7 and 8 genes result in enhanced SL signaling, which in turn might promote stomatal closure and consequently drought resistance. Indeed, increasing evidence has indicated the promoting roles of SLs and SL signaling in stomatal closing [15,16,[18][19][20][21]59], further supporting the involvement of SMXL 6, 7 and 8 repressors in regulating stomatal movement through the SL signaling. In addition, various SL-deficient plant species have shown slower stomatal closing rates in the presence of ABA than WT plants [16,20,21], and reduced ABA sensitivity in stomatal response assays, compared with WT [20,21], suggesting the existence of an ABA-dependent mediation of stomatal closure by SLs and SL signaling.…”

“…Previous investigations reported that SMXL6, 7 and 8 genes redundantly regulate shoot branching and leaf morphology as the members of SL signaling [6,7]. However, compelling evidence for the functions of SMXL6, 7 and 8 genes in other phenotypes controlled by SL signaling, such as leaf senescence, secondary growth and drought resistance [7,19,21], is still lacking. In the present study, by comparing drought resistance levels of various combinations of knock-out mutants of SMXL6, 7 and 8 genes, including single, double and triple mutants (Figure 1; Figure S1), we firmly showed that SMXL6, 7 and 8 are involved in regulating drought resistance in Arabidopsis plants as redundant negative regulators.…”

“…For instance, SL-depleted (e.g., max3 and max4) and SL-receptor (e.g., d14) Arabidopsis mutant plants, and SL-depleted L. japonicus (e.g., LjCCD7-silenced) and tomato (e.g., SlCCD7-silenced) transgenic plants were shown to exhibit susceptible phenotypes to various water-deficit stress conditions [16][17][18][19][20][21]. Additionally, the differential level in drought resistance of smxl6,7,8 mutant versus WT (6.2-8.6-fold differences in survival rate of smxl6,7,8 mutant, compared with WT plants; Figure 1 and Figure S1) was much higher than the previously reported differential level in drought susceptibility of d14 mutant versus WT (1.7-2.2-fold differences in survival rate of WT, compared with d14 mutant plants) [19], suggesting that the SMXL6, 7 and 8 repressors might act in other pathway(s) through a yet-unknown 'promiscuity' in the interaction dynamics to regulate plant response to drought.…”

“…Recent investigations in various plant species reported positive roles of SLs in drought resistance through functional analyses of various mutants with defect in SL-biosynthetic or SL positive regulatory genes, such as the Arabidopsis SL-biosynthetic max3 and max4 and SL-signaling max2 and d14 mutant plants [15][16][17][18][19], and the Lotus japonicus and tomato (Solanum lycopersicum) SL-depleted transgenic plants silenced for a MAX3 homolog, named CAROTENOID CLEAVAGE DIOXYGENASE 7 (CCD7) gene [3,20,21]. Physiological and biochemical analyses of these mutants in relation to drought stress revealed that SL signaling regulates a number of drought-related mechanisms, including water transpiration, abscisic acid (ABA) responsiveness, leaf senescence, cell membrane integrity and anthocyanin biosynthesis [15][16][17][18][19][20][21]. However, the roles of the negative regulators SMXL6, 7 and 8 and associated mechanisms underlying drought resistance are still unknown.…”