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

Weiqiang Li,Lam-Son Phan Tran,Yuchen Miao,Xiaojian Yin,Chunjie Tian,Yong Yang,Yasuko Watanabe,Kun Li,Kien Huu Nguyen,Shinjiro Yamaguchi,Cuong Duy Tran,Jinggong Guo

doi:10.3390/biom10040607

Abstract

Previous investigations have shown that the SUPPRESSORS OF MAX2 1-LIKE6, 7 and 8 (SMXL6, 7 and 8) proteins redundantly repress strigolactone (SL) signaling in plant growth and development. Recently, a growing body of evidence indicated that SLs positively regulate plant drought resistance through functional analyses of genes involved in SL biosynthesis and positive regulation of SL signaling. However, the functions of the SL-signaling negative regulators SMXL6, 7 and 8 in drought resistance and the associated mechanisms remain elusive. To reveal the functions of these SMXL proteins, we analyzed the drought-resistant phenotype of the triple smxl6,7,8 mutant plants and studied several drought resistance-related traits. Our results showed that the smxl6,7,8 mutant plants were more resistant to drought than wild-type plants. Physiological investigations indicated that the smxl6,7,8 mutant plants exhibited higher leaf surface temperature, reduced cuticle permeability, as well as decreases in drought-induced water loss and cell membrane damage in comparison with wild-type plants. Additionally, smxl6,7,8 mutant plants displayed an increase in anthocyanin biosynthesis during drought, enhanced detoxification capacity and increased sensitivity to abscisic acid in cotyledon opening and growth inhibition assays. A good correlation between the expression levels of some relevant genes and the examined physiological and biochemical traits was observed. Our findings together indicate that the SMXL6, 7 and 8 act as negative regulators of drought resistance, and that disruption of these SMXL genes in crops may provide a novel way to improve their drought resistance.

Highlights

Strigolactones (SLs) are a new member of plant hormones, regulating plant growth and development, and plant responses to environmental stresses [1,2,3,4]
Our results showed that the mutations of SMXL6, 7 and 8 genes in Arabidopsis enhanced plant drought resistance of the smxl6,7,8 mutant plants through preventing leaf water loss, enhancing abscisic acid (ABA) responsiveness, and promoting anthocyanin biosynthesis and reactive oxygen species (ROS)-scavenging activities
We hypothesized that ROS homeostasis might be affected in smxl6,7,8 mutant plants; and we investigated the accumulation of O2.– and H2O2 using nitro blue tetrazolium (NBT) and DAP stainings, respectively

Summary

Introduction

Strigolactones (SLs) are a new member of plant hormones, regulating plant growth and development, and plant responses to environmental stresses [1,2,3,4]. In Arabidopsis, the SL signaling pathway comprises of two positive regulators Arabidopsis D14 protein (D14) and MAX2, and three redundant negative regulators SUPPRESSOR OF MAX2 1-LIKE6, 7 and 8 (SMXL6, 7 and 8) [1,4,6,7]. The newly formed D14-MAX2-SCF complex polyubiquitinates the three redundant SMXL6, 7 and 8 repressors, and triggers the degradation of these negative regulators, releasing SL-responsive genes and resulting in SL-regulated phenotypes associated with shoot branching, lateral root growth, primary root growth and leaf shape, etc. Mutations of all three SMXL6, 7 and 8 genes in max and max backgrounds suppressed max and max shoot branching, and leaf shape and lateral root phenotypes that are associated with the SL signaling [6,7]. It is worth mentioning that the MAX2 protein plays a central role in a sister pathway mediated by a D14 homolog called KARRIKIN-INSENSITIVE2 (KAI2) that receives signals from karrikins (KARs) found in smoke [2]

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Discussion

Conclusion