Biology subjects

Yoshida, M. W.

Publications and source records attributed to Yoshida, M. W..

4 recordsLinked to original sources

bioRxiv2023

Physcomitrella SUN2 mediates MTOC association to the nuclear envelope and facilitates chromosome alignment during spindle assembly

Plant cells lack centrosomes and instead utilise acentrosomal microtubule organising centres (MTOCs) to rapidly increase the number of microtubules at the onset of spindle assembly. Although several proteins required for MTOC formation have been identified, how the MTOC is positioned at the right place is not known. Here, we show that the inner nuclear membrane protein SUN2 is required for MTOC association with the nuclear envelope (NE) during mitotic prophase in the moss Physcomitrium patens. In actively dividing protonemal cells, microtubules accumulate around the NE during prophase. In particular, regional MTOC is formed at the apical surface of the nucleus. However, microtubule accumulation around the NE was impaired and apical MTOCs were mislocalised in sun2 knockout (KO) cells. In addition, chromosome distribution in the nucleus was skewed, suggesting that SUN2 mediates the linking of microtubules with chromosomes. Upon nuclear envelope breakdown (NEBD), the mitotic spindle was assembled with mislocalised MTOC, which were a source of microtubules in sun2 KO plants. However, completion of chromosome alignment in the spindle was delayed; in severe cases, the chromosome was transiently detached from the spindle body. SUN2 tended to localise to the apical surface of the nucleus during prophase in a microtubule-dependent manner. Based on these results, we propose that SUN2 facilitates the attachment of microtubules to chromosomes during spindle assembly by linking them prior to NEBD. Furthermore, this study suggests that trans-NE microtubule-chromosome linking, a well-known function of SUN in animals and yeast, is conserved in plants.

plant biology↗

bioRxiv2022

Armadillo repeat-containing kinesin represents the versatile plus-end-directed transporter in plants

Kinesin-1, also known as conventional kinesin, is widely utilised for microtubule plus-end-directed ("anterograde") transport of various cargos in animal cells. However, a motor functionally equivalent to the conventional kinesin has not been identified in plants, which lack the kinesin-1 genes. Here, we show that plant-specific armadillo repeat-containing kinesin (ARK) is the long sought-after versatile anterograde transporter in plants. In ARK mutants of the moss Physcomitrium patens, the anterograde motility of nuclei, chloroplasts, mitochondria, and secretory vesicles was suppressed. Ectopic expression of non-motile or tail-deleted ARK did not restore organelle distribution. Another prominent macroscopic phenotype of ARK mutants was the suppression of cell tip growth. We showed that this defect was attributed to the mislocalisation of actin regulators, including RopGEFs; expression and forced apical localisation of RopGEF3 suppressed the growth phenotype of the ARK mutant. The mutant phenotypes were partially rescued by ARK homologues in Arabidopsis thaliana, suggesting the conservation of ARK functions in plants.

cell biology↗

bioRxiv2020

Spindle position dictates division site during asymmetric cell division in moss

Asymmetric cell division (ACD) underlies the development of multicellular organisms. It is considered that the division site in land plants is predetermined prior to mitosis and that the localization of the mitotic spindle does not govern the division plane. This contrasts with animal ACD, in which the division site is defined by active spindle-positioning mechanisms. Here, we isolated a hypomorphic mutant of the conserved microtubule-associated protein TPX2 in the moss Physcomitrium patens and observed abnormal spindle motility during cell division. This defect compromised the position of the division site and produced inverted daughter cell sizes in the first ACD of gametophore (leafy shoot) development. The phenotype was rescued by restoring endogenous TPX2 function and, unexpectedly, by depolymerizing actin filaments. Thus, we have identified an active spindle-positioning mechanism that, reminiscent of acentrosomal ACD in animals, involves microtubules and actin filaments and sets the division site in plants.

plant biology↗

bioRxiv2019

Critical domains of moss KCBP kinesin for cargo transport

KCBP is a microtubule (MT) minus-end-directed kinesin widely conserved in plants. It was shown in Arabidopsis that KCBP controls trichome cell shape by orchestrating MT and actin cytoskeletons using its tail and motor domains. In contrast, the KCBP knockout (KO) line in the moss Physcomitrella patens showed a defect in nuclear and organelle positioning in apical stem cells. Moss KCBP is postulated to transport the nucleus and chloroplast via direct binding to their membranes, since it binds to and transports liposomes composed of phospholipids in vitro. However, domains required for cargo transport in vivo have not been mapped. Here, we performed a structure-function analysis of moss KCBP. We found that the FERM domain in the tail region, which is known to bind to lipids as well as other proteins, is essential for both nuclear and chloroplast positioning, whereas the proximal MyTH4 domain plays a supporting role in chloroplast transport. After anaphase but prior to nuclear envelope re-formation, KCBP accumulates on the chromosomes, in particular at the centromeric region in a FERM-dependent manner. In the KCBP knockout line, poleward chromosome motility in anaphase was reduced and lagging chromosomes occasionally appeared. These results suggest that KCBP binds to non-membranous naked chromosomes via an unidentified protein(s) for their transport. Finally, the liverwort orthologue of KCBP rescued the chromosome/chloroplast mis-positioning of the moss KCBP KO line, suggesting that the cargo transport function is conserved at least in bryophytes.

plant biology↗