Class XI Myosins Contribute to Auxin Response and Senescence-Induced Cell Death in Arabidopsis.

Eve-Ly Ojangu,Birger Ilau,Kristiina Talts,Eliis Ihoma,Valerian V Dolja,Heiti Paves,Krista Tanner,Erkki Truve

doi:10.3389/fpls.2018.01570

Eve-Ly Ojangu, Birger Ilau + Show 6 more

Open Access

https://doi.org/10.3389/fpls.2018.01570

Copy DOI

Abstract

The integrity and dynamics of actin cytoskeleton is necessary not only for plant cell architecture but also for membrane trafficking-mediated processes such as polar auxin transport, senescence, and cell death. In Arabidopsis, the inactivation of actin-based molecular motors, class XI myosins, affects the membrane trafficking and integrity of actin cytoskeleton, and thus causes defective plant growth and morphology, altered lifespan and reduced fertility. To evaluate the potential contribution of class XI myosins to the auxin response, senescence and cell death, we followed the flower and leaf development in the triple gene knockout mutant xi1 xi2 xik (3KO) and in rescued line stably expressing myosin XI-K:YFP (3KOR). Assessing the development of primary inflorescence shoots we found that the 3KO plants produced more axillary branches. Exploiting the auxin-dependent reporters DR5::GUS and IAA2::GUS, a significant reduction in auxin responsiveness was found throughout the development of the 3KO plants. Examination of the flower development of the plants stably expressing the auxin transporter PIN1::PIN1-GFP revealed partial loss of PIN1 polarization in developing 3KO pistils. Surprisingly, the stable expression of PIN1::PIN1-GFP significantly enhanced the semi-sterile phenotype of the 3KO plants. Further we investigated the localization of myosin XI-K:YFP in the 3KOR floral organs and revealed its expression pattern in floral primordia, developing pistils, and anther filaments. Interestingly, the XI-K:YFP and PIN1::PIN1-GFP shared partially overlapping but distinct expression patterns throughout floral development. Assessing the foliar development of the 3KO plants revealed increased rosette leaf production with signs of premature yellowing. Symptoms of the premature senescence correlated with massive loss of chlorophyll, increased cell death, early plasmolysis of epidermal cells, and strong up-regulation of the stress-inducible senescence-associated gene SAG13 in 3KO plants. Simultaneously, the reduced auxin responsiveness and premature leaf senescence were accompanied by significant anthocyanin accumulation in 3KO tissues. Collectively, our results provide genetic evidences that Arabidopsis class XI myosins arrange the flower morphogenesis and leaf longevity via contributing to auxin responses, leaf senescence, and cell death.

Highlights

The dynamics of actin cytoskeleton, including filament assembly, disassembly and reorganization are regulated by diverse actin binding proteins (ABPs)
Our results show that the three Arabidopsis class XI myosins, XI-1, XI-2, and XI-K, contribute to the auxin responses and cell death, and thereby affect developmental decisions during flower growth and leaf senescence
Using triple mutant line 3KO (Ojangu et al, 2012) and complemented line 3KOR (Peremyslov et al, 2012), we demonstrate that simultaneous depletion of these three myosins affects responsiveness of the auxin-dependent promoters and polarization of the PIN1 auxin efflux carrier, causes premature onset of senescence and cell death in leaves, elevates accumulation of anthocyanins, and changes the expression levels of genes related to these processes

Summary

Introduction

The dynamics of actin cytoskeleton, including filament assembly, disassembly and reorganization are regulated by diverse actin binding proteins (ABPs). The stature of myosin XI single, double, triple, quadruple and quintuple knockout plants is decreased progressively along with the reduction in cell size (Ojangu et al, 2007, 2012; Peremyslov et al, 2008, 2010; Prokhnevsky et al, 2008; Ueda et al, 2010; Park and Nebenführ, 2013; Cai et al, 2014; Madison et al, 2015; Abu-Abied et al, 2018). In the 3KO, cytoplasmic streaming is virtually arrested, the elongation of epidermal and other cell types is decreased and plant size and fertility is affected (Peremyslov et al, 2010; Ueda et al, 2010; Ojangu et al, 2012; Cai et al, 2014; Scheuring et al, 2016)

Methods

Results

Conclusion