Arabidopsis thaliana myosin XIK is involved in root hair as well as trichome morphogenesis on stems and leaves

Abstract

Myosins form a large superfamily of molecular motors that move along actin filaments. The functions of myosins in plant cells are thought to be related to various processes: cell division, movement of mitochondria and chloroplasts, cytoplasmic streaming, rearrangement of transvacuolar strands, and statolith positioning. Class VIII and XI myosins are represented in the Arabidopsis thaliana genome by 4 and 13 potential genes, respectively. The roles of individual class XI myosins and their cellular targets in A. thaliana are still unclear. In this work we implemented a reverse genetic approach to analyse the loss-of-function mutants of XIK, a representative of class XI myosins in A. thaliana. Three different T-DNA insertion mutants in the myosin XIK gene showed similar phenotypes: impaired growth of root hair cells, twisted shape of stem trichomes, and irregular size, branch positioning, and branch expansion of leaf trichomes. Morphometric analysis of mutant seedlings showed that the average length of root hairs was reduced up to 50% in comparison with wild-type root hairs, suggesting an involvement of the class XI myosin XIK in tip growth. On leaves, the proportion of trichomes with short branches was doubleed in mutant plants, and the mutant trichomes possessed a mildly twisted shape. Therefore, we concluded that myosin XIK is involved also in the elongation of stalks and branches of trichomes.

Root Hairs

“…The Arabidopsis genome contains 13 myosin XI genes (Reddy and Day, 2001). Reduced root hair growth and altered actin organization is observed in the MYOSIN XI K (ATXIK: At5g20490) mutant (Park and Nebenfuhr, 2013), as well as lines in which multiple myosin XI genes are disrupted (Ojangu et al, 2007;Prokhnevsky et al, 2008;Peremyslov et al, 2008;Peremyslov et al 2010). Also, myosin XI motor activity is decreased under high Ca 2+ conditions (Tominaga et al, 2012), resulting in reduced cytoplasmic streaming velocities (Doree and Picard, 1980;Woods et al, 1984;Takagi and Nagai, 1986;Kohno and Shimmen, 1988).…”

Class XI Myosins Are Required for Development, Cell Expansion, and F-Actin Organization in Arabidopsis

“…These myosins were also implicated in endoplasmic reticulum (ER) streaming (Ueda et al, 2010) and remodeling (Sparkes et al, 2009a) as well as in plastid dynamics (Natesan et al, 2009;Sattarzadeh et al, 2009). In addition, some class XI myosins play a role in root hair elongation (Ojangu et al, 2007;Peremyslov et al, 2008;Prokhnevsky et al, 2008). Interestingly, whereas yeast and vertebrates possess only two or three class V myosins, the number of class XI myosins in plants is much higher, with 13 present in Arabidopsis thaliana (Reddy and Day, 2001).…”

A Comparative Study of the Involvement of 17 Arabidopsis Myosin Family Members on the Motility of Golgi and Other Organelles

“…In contrast, the association of the single globular tail domain of MYA1 or MYA2 with peroxisomes did not arrest their motility (Li and Nebenfü hr, 2007). Knockout plants for myosin xi-k and mya2 had root hair phenotypes (Ojangu et al, 2007;Peremyslov et al, 2008); however, all other 11 myosin XI single knockouts looked normal under regular growth conditions . Reciprocal stimulation between dimerization via the coiled-coil domains of MYA1 and organelle binding was suggested (Li and Nebenfü hr, 2008a).…”