A New Allele of the SPIKE1 Locus Reveals Distinct Regulation of Trichome and Pavement Cell Development and Plant Growth.

Shuang Liang,Fei Yu,Xiayan Liu,Lijun An,Jun Zhao,Jingxia Shao,Yafei Qi,Xuying Yang,Meng Deng

doi:10.3389/fpls.2019.00016

Shuang Liang, Fei Yu + Show 7 more

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https://doi.org/10.3389/fpls.2019.00016

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Abstract

The single-celled trichomes of Arabidopsis thaliana have long served as an elegant model for elucidating the mechanisms of cell differentiation and morphogenesis due to their unique growth patterns. To identify new components in the genetic network that governs trichome development, we carried out exhaustive screens for additional Arabidopsis mutants with altered trichome morphology. Here, we report one mutant, aberrantly branched trichome1-1 (abt1-1), with a reduced trichome branching phenotype. After positional cloning, a point mutation in the SPIKE1 (SPK1) gene was identified in abt1-1. Further genetic complementation experiments confirmed that abt1-1 is a new allele of SPK1, so abt1-1 was renamed as spk1-7 according to the literatures. spk1-7 and two other spk1 mutant alleles, covering a spectrum of phenotypic severity, highlighted the distinct responses of developmental programs to different SPK1 mutations. Although null spk1 mutants are lethal and show defects in plant stature, trichome and epidermal pavement cell development, only trichome branching is affected in spk1-7. Surprisingly, we found that SPK1 is involved in the positioning of nuclei in the trichome cells. Lastly, through double mutant analysis, we found the coordinated regulation of trichome branching between SPK1 and two other trichome branching regulators, ANGUSTIFOLIA (AN) and ZWICHEL (ZWI). SPK1 might serve for the precise positioning of trichome nuclei, while AN and ZWI contribute to the formation of branch points through governing the cMTs dynamics. In summary, this study presented a fully viable new mutant allele of SPK1 and shed new light on the regulation of trichome branching and other developmental processes by SPK1.

Highlights

The differentiation of distinct cell types is one of the most fundamental features of multicellular organisms (Lee and Schiefelbein, 2002)
In our ongoing effort to identify new factors that define trichome morphology, we carried out large-scale Ethyl methanesulfonate (EMS)-mutagenesis and a trichome branching defective mutant, designated abt1-1 was isolated
The reduced trichome branching phenotype in abt1-1 was more pronounced in the fifth rosette leaves than in the third rosette leaves as we observed an average of 68% of two-branched trichomes in the third leaves (Figure 1D) versus an average of 76% of two-branched in the fifth leaves (Figure 1E)

Summary

Introduction

The differentiation of distinct cell types is one of the most fundamental features of multicellular organisms (Lee and Schiefelbein, 2002). In model plant Arabidopsis thaliana, leaf trichomes are unicellular structures usually bearing three or four branches (Hülskamp et al, 1994), and numerous pathways that control trichome branching have been identified in the last two decades (Folkers et al, 1997; Hülskamp, 2004; Guimil and Dunand, 2007; Ishida et al, 2008; Yang and Ye, 2013). The number of trichome branches is closely linked with plant cell cycle control (Schnittger and Hülskamp, 2002; Kasili et al, 2010; Yang and Ye, 2013). A myriads of mutants including kaktus, spindly, polycomb, triptychon, rastifari, and rpt2a showed extended endoreplication and elevated ploidy, and displayed hyperbranched trichomes, suggesting a certain degree of correlation between trichome branching and endoreplication (Szymanski and Marks, 1998; Perazza et al, 1999; Sonoda et al, 2009). The correlation between branching and ploidy and nuclear DNA content cannot be extrapolated to all trichome branching mutants, implicating that additional pathways are involved in the elaboration of trichome branching (Ilgenfritz et al, 2003)

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