Editors' ChoicePlant Development

Fitting Cells Together

STKE  15 Mar 2005:
Vol. 2005, Issue 275, pp. tw95
DOI: 10.1126/stke.2752005tw95

Fu et al. investigated the role of the ROP2 and ROP4 guanosine triphosphatases (ROP2/4; plant-specific Rho-family GTPases) in leaf cell morphogenesis and found that cell shape depended on two antagonistic ROP-mediated pathways. Arabidopsis leaf pavement cells grow in a jigsaw puzzle-like pattern, with lobes from one cell fitting into indentations (necks) on its neighbors. Inhibition of ROP2 with RNA interference (RNAi) in a ROP4 knockout mutant attenuated lobe development. Cortical microfilaments (associated with expanding regions of wild-type cells) were absent in cells lacking ROP2/4, whereas bundles of microtubules, normally associated only with neck regions, were found throughout the cell. ROP-interactive CRIB-motif-containing protein 4 (RIC4) was located at incipient lobes and lobe tips of wild-type cells, whereas expression of activated ROP2 [which interacted with RIC4 as monitored by fluorescence resonance energy transfer (FRET) analysis] caused RIC4 to distribute throughout the cell cortex. RIC4 overexpression enhanced microfilament accumulation and distribution, whereas RIC4 knockdown reduced microfilament accumulation and attenuated lobe formation. In contrast, RIC1, a ROP target that localized with microtubules, promoted microtubule bundling and inhibited lobe expansion. Plasma membrane-associated activated ROP2 bound to RIC1 and sequestered it from microtubules. FRET analysis together with evaluation of various mutant combinations indicated that RIC1 inhibited the interaction between ROP2 and RIC4, antagonizing their promotion of microfilament accumulation and lobe development; depolymerization experiments indicated that this depended at least in part on RIC1 promotion of microtubule organization. Thus, localized activation of ROP2/4, together with its regulation of the two antagonistic pathways, appears to define regions of the cell that form lobes and regions that form indentations. Settleman discusses the research in a Preview and comments on its relevance to animal development.

Y. Fu, Y. Gu, Z. Zheng, G. Wasteneys, Z. Yang, Arabidopsis interdigitating cell growth requires two antagonistic pathways with opposing action on cell morphogenesis. Cell 120, 687-700 (2005). [Online Journal]

J. Settleman, Intercalating Arabidopsis leaf cells: A jigsaw puzzle of lobes, necks, ROPs, and RICs. Cell 120, 570-572 (2005). [Online Journal]