KCH kinesin drives nuclear transport and cytoskeletal coalescence for tip cell growth

Abstract

Long-distance transport along microtubules (MTs) is critical for intracellular organisation. In animals, antagonistic motor proteins kinesin (plus end-directed) and dynein (minus end-directed) drive cargo transport. In land plants, however, the identity of motors responsible for transport is poorly understood, as genes encoding cytoplasmic dynein are missing. How other functions of dynein are brought about in plants also remains unknown. Here, we show that a subclass of the kinesin-14 family, KCH-which can also bind actin-drives MT minus end-directed nuclear transport in the moss Physcomitrella patens. When all four KCH genes were deleted, the nucleus was not maintained in the cell centre but was translocated to the apical end of protonemal cells. In the knockout (KO) line, apical cell tip growth was also severely suppressed. KCH was localised on MTs, including at the MT focal point near the tip where MT plus ends coalesced with actin filaments. MT focus was not persistent in KCH KO lines, whereas actin destabilisation also disrupted the focus despite KCH remaining on unfocused MTs. Functions of nuclear transport and tip growth were distinct, as a truncated KCH construct restored nuclear transport activity but not tip growth retardation of the KO line. Thus, our study identified KCH as a long-distance retrograde transporter as well as a cytoskeletal crosslinker, reminiscent of the versatile animal dynein.

Characterisation of rapid alkalinisation factors in Physcomitrium patens reveals functional conservation in tip growth

“…7c,d; Tables S5, S6). Notably Cellular Compartments of ‘kinesin complex’ (GO: 0005871) and ‘microtubule associated complex’ (GO: 0005875) that facilitated tip growth in P. patens were also enriched (Hiwatashi et al ., 2014; Yamada & Goshima, 2018), supporting our claim that PpRALF1 and PpRALF2 are involved in tip growth.…”

“…7c,d; Tables S5, S6). Notably Cellular Compartments of 'kinesin complex' (GO: 0005871) and 'microtubule associated complex' (GO: 0005875) that facilitated tip growth in P. patens were also enriched (Hiwatashi et al, 2014;Yamada & Goshima, 2018), supporting our claim that PpRALF1 and PpRALF2 are involved in tip growth. While a range of biological process GO terms in biosynthesis and metabolic turnover processes were enriched in both PpRALFs, we detected distinct Molecular Function GO terms between PpRALF1 and PpRALF2.…”

The Plant Cytoskeleton and Crosslinking Factors

“…MF and MT are able to respond to abiotic stress and AtKCH3 was involved in the regulation of abiotic stress response by regulating the dynamic changes of MF and MT. KCH transports nucleation and MT-actin interactions in flowering plants [56]. The results of low-speed coprecipitation showed that CH domain of AtKCH3 and AtKCH4 could promote MF bunching in vitro [57].…”

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

“…In this system, when plus-end-directed motility is predominant over minus-end-directed motility, the organelle moves apically and is abundant on the apical side, and vice versa. Based on this advantage, several kinesin-14 family members have been identified as the drivers of retrograde transport, namely KCH for the nucleus, KCBP for the chloroplast and telophase chromosome, and ATK for newly formed microtubules [24][25][26] . Studies in P. patens thus drew a functional analogy between kinesin-14s and dynein and further illustrated the contribution of intracellular transport driven by the microtubule-kinesin mechanism.…”