RICE MORPHOLOGY DETERMINANTEncodes the Type II Formin FH5 and Regulates Rice Morphogenesis    

Abstract

Multicellular organisms contain a large number of formins; however, their physiological roles in plants remain poorly understood. Here, we reveal that formin homology 5 (FH5), a type II formin mutated in rice morphology determinant (rmd), plays a crucial role in determining rice (Oryza sativa) morphology. FH5/RMD encodes a formin-like protein consisting of an N-terminal phosphatase tensin (PTEN)-like domain, an FH1 domain, and an FH2 domain. The rmd mutants display a bending growth pattern in seedlings, are stunted as adult plants, and have aberrant inflorescence (panicle) and seed shape. Cytological analysis showed that rmd mutants have severe cell elongation defects and abnormal microtubule and microfilament arrays. FH5/RMD is ubiquitously expressed in rice tissues, and its protein localization to the chloroplast surface is mediated by the PTEN domain. Biochemical assays demonstrated that recombinant FH5 protein can nucleate actin polymerization from monomeric G-actin or actin/profilin complexes, cap the barbed end of actin filaments, and bundle actin filaments in vitro. Moreover, FH5 can directly bind to and bundle microtubules through its FH2 domain in vitro. Our findings suggest that the rice formin protein FH5 plays a critical role in determining plant morphology by regulating actin dynamics and proper spatial organization of microtubules and microfilaments.

Rice TUTOU1 Encodes a Suppressor of cAMP Receptor-Like Protein That Is Important for Actin Organization and Panicle Development

“…F-actin was stained using the previously described method (Olyslaegers and Verbelen, 1998;Yang et al, 2011;Zhang et al, 2011). Mature rice leaves were incubated in PEM buffer (100 mM PIPES, 10 mM EGTA, 0.3 M mannitol, and 5 mM MgSO 4 , pH 6.9) and 0.66 mM Alexa Fluor 488-phalloidin (Life Technologies).…”

Rice Morphology Determinant-Mediated Actin Filament Organization Contributes to Pollen Tube Growth

“…Even though loss of function of RMD caused abnormal pollen tube growth, the seed setting of the mutant seems normal, possibly due to the excessive number of pollen grains during fertilization (Supplemental Fig. S1I; Zhang et al, 2011). This observation also suggests the major role of RMD in rapid tip growth instead of fertilization.…”

“…S6B), which is consistent with the immunolabeling assay using JIM7 antibody. By contrast, pollen tubes of rmd mutants and RNAi lines (Ri-S; Zhang et al, 2011) exhibited staining spots in the tip region as well as regions distal to the tip (Supplemental Fig. S6B).…”

“…S1, E-G). Despite the change in panicle architecture, rmd-1 and rmd-2 (another mutant allele of RMD; Zhang et al, 2011) plants could generate seeds with a similar seedsetting rate to that of the wild type after fertilization (Supplemental Fig. S1, H-I), although the seed shape was altered in the mutants (Supplemental Fig.…”

“…Our previous work demonstrated that a type II formin protein, RICE MORPHOLOGY DETERMINANT (RMD; also called BENT UPPERMOST INTERNODE1) from rice (Oryza sativa), functionally regulates cytoskeleton organization by nucleating, capping, and bundling actin in vitro and also plays a crucial role in regulating F-actin dynamics and arrays in rice cells (Yang et al, 2011;Zhang et al, 2011;Li et al, 2014). rmd mutants exhibit altered microfilament and microtubule arrays, causing defective plant morphology .…”