1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 IntroductionThe growth and morphogenesis of plant cells relies on the orientation of cellulose microfibrils and cortical microtubules. Microtubules are cytoskeletal polymers composed of α-and β-tubulin heterodimers. Microtubules are polarized with a fast growing plus end and a slow growing minus end, and exhibit dynamic behaviors such as rapid growth and shrinkage both in vivo and in vitro (Mitchison and Kirschner 1984; Horio and Hotani 1986; Sammak and Borisy 1988; Shaw et al. 2003;Nakamura et al. 2004). Cortical microtubules are specifically found in plant cells during interphase and are localized close to the cell cortex (Ledbetter and Porter 1963). Cortical microtubules align perpendicularly to the growth direction and regulate anisotropic growth and morphogenesis of rapidly expanding cells (Green 1962; Shibaoka 1994;Wasteneys 2002; Fig. 1). Findings from genetic studies of Arabidopsis thaliana mutants strongly support the essential roles of cortical microtubule arrays on directional cell growth (Whittington et al. 2001; Thitamadee et al. 2002; Abe et al. 2004; Ishida et al. 2007a; Ishida et al. 2007b; Sedbrook and Kaloriti 2008;Wasteneys and Ambrose 2009). In addition, microtubules regulate cell division and chromosome segregation. In the mitotic phase, microtubules form a series of arrays; a preprophase band that determines the future cell division plane, mitotic spindle that segregate chromosomes, and a phragmoplast that constructs the new cell plate ( 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 suggesting that cortical microtubules could also regulate directional cell growth independently of cellulose microfibrils (Sugimoto et al. 2003). Fujita et al. (2011) have shown that cortical microtubule abundance affects cellulose crystallinity to promote directional cell growth.Microtubules might regulate the mobility and stability of cellulose synthase complexes to affect physical properties of cellulose microfibrils. Because it is beyond the scope of this review, Interested readers could consult the recent literature and references therein (Bringmann et al. 2012; Fujita et al. 2012; Lei et al. 2014). In this review, we will summarize recent findings on microtubule regulation with focus on phosphorylation-dependent regulatory mechanisms. Microtubule regulationMicrotubule-associated proteins (MAPs) play pivotal roles in the regulation of microtubule dynamics (Hamada 2014). MAPs affect microtubule assembly and bundling and regulate their geometry and organization. Because the function and regulation of MAPs have been well described in detail, we show here a few examples from a cellular and developmen...

Regulation of the stability and the quality of mitochondrial RNA is essential for the maintenance of mitochondrial and cellular functions in eukaryotes. We have previously reported that the eukaryotic poly(A)-specific ribonuclease (PARN) and the prokaryotic poly(A) polymerase encoded by AHG2 and AGS1, respectively, coordinately regulate the poly(A) status and the stability of mitochondrial mRNA in Arabidopsis. Mitochondrial function of PARN has not been reported in any other eukaryotes. To know how much this PARN-based mitochondrial mRNA regulation is conserved among plants, we studied the AHG2 and AGS1 counterparts of the liverwort, Marchantia polymorpha, a member of basal land plant lineage. We found that M. polymorpha has one ortholog each for AHG2 and AGS1, named MpAHG2 and MpAGS1, respectively. Their Citrine-fused proteins were detected in mitochondria of the liverwort. Molecular genetic analysis showed that MpAHG2 is essential and functionally interacts with MpAGS1 as observed in Arabidopsis. A recombinant MpAHG2 protein had a deadenylase activity in vitro. Overexpression of MpAGS1 and the reduced expression of MpAHG2 caused an accumulation of polyadenylated Mpcox1 mRNA. Furthermore, MpAHG2 suppressed Arabidopsis ahg2-1 mutant phenotype. These results suggest that the PARN-based mitochondrial mRNA regulatory system is conserved in land plants.

The bdelloid rotifer of the genus Adineta is a freshwater metazoan characterized by anhydrobiosis, a highly stable state of suspended animation induced by desiccation. This study investigated the influence of anhydrobiosis on the thermal habituation by use of an index, Activity Ratio (AR = the number of active rotifers at each experimental temperature/ number of active rotifers at the 25°C stage). In the first experiment, rotifers were divided into two groups: one group was cultivated at 25°C throughout experiment, and another group was transferred to 15°C for two days. AR was estimated during heating up to 40°C, or during cooling down to 5°C in each group. The largest difference in AR occurred at 35°C and 10°C, indicating that AR was changed depending on the pretreated medium temperature. In the next experiment, rotifers were maintained at 15°C, and were desiccated (anhydrobiosis). AR was estimated in the high temperature range (25°C to 40°C), using rotifers that had recovered from anhydrobiosis. AR was significantly different between the groups with and without desiccation, suggesting that thermal habituation at 15°C was completely cancelled by anhydrobiosis. Possible mechanisms on the influence of anhydrobiosis on the thermal habituation have been discussed in terms of neural changes and proteins.