Two Seven-Transmembrane Domain MILDEW RESISTANCE LOCUS O Proteins Cofunction inArabidopsisRoot Thigmomorphogenesis  

Abstract

Directional root expansion is governed by nutrient gradients, positive gravitropism and hydrotropism, negative phototropism and thigmotropism, as well as endogenous oscillations in the growth trajectory (circumnutation). Null mutations in phylogenetically related Arabidopsis thaliana genes MILDEW RESISTANCE LOCUS O 4 (MLO4) and MLO11, encoding heptahelical, plasma membrane-localized proteins predominantly expressed in the root tip, result in aberrant root thigmomorphogenesis. mlo4 and mlo11 mutant plants show anisotropic, chiral root expansion manifesting as tightly curled root patterns upon contact with solid surfaces. The defect in mlo4 and mlo11 mutants is nonadditive and dependent on light and nutrients. Genetic epistasis experiments demonstrate that the mutant phenotype is independently modulated by the Gb subunit of the heterotrimeric G-protein complex. Analysis of expressed chimeric MLO4/MLO2 proteins revealed that the C-terminal domain of MLO4 is necessary but not sufficient for MLO4 action in root thigmomorphogenesis. The expression of the auxin efflux carrier fusion, PIN1-green fluorescent protein, the pattern of auxin-induced gene expression, and acropetal as well as basipetal auxin transport are altered at the root tip of mlo4 mutant seedlings. Moreover, addition of auxin transport inhibitors or the loss of EIR1/AGR1/PIN2 function abolishes root curling of mlo4, mlo11, and wild-type seedlings. These results demonstrate that the exaggerated root curling phenotypes of the mlo4 and mlo11 mutants depend on auxin gradients and suggest that MLO4 and MLO11 cofunction as modulators of touch-induced root tropism.

Genome-wide Identification, Classification and Expression Analysis of the Mildew Resistance Locus O ( MLO ) Gene Family in Sweet Orange ( Citrus sinensis )

“…tomato and Xanthomonas campestris pv. vesicatoria [ 60,61 ]; wounding [ 21,37,62 ]; phytohormone [ 24,26,63 ] and abiotic stresses [ 63,64 ]. As a rule, however, the paralogs in MLO family, as illuminated by their clustering pattern (Fig.…”

“…2), AtMLO4/11 referred to the regulation of root thigmomorphogenesis in Arabidopsis, however, the closely paralogous AtMLO14 gene does not participate in this plant growth process, since no obvious variant phenotype was displayed in the AtMLO14 mutant [ 26,59 ]. CisMLO3/8 were assembled in clade III together with the five Arabidopsis proteins AtMLO5/7/8/9/10 representing the functional clade with AtMLO7 protein responsible for similar functions of pollen tube perception of the female germ cell in Arabidopsis [ 27 ].…”

Cytokinin Interplay with Ethylene, Auxin, and Glucose Signaling Controls Arabidopsis Seedling Root Directional Growth

“…Root plasticity is important for the optimal positioning of plants with respect to the changing microenvironment and facilitates growth of the root via the easiest route through the soil. Among the other factors, changes in auxin, ethylene, gravity signaling, or alteration in cell wall properties cause altered root directional growth (Okada and Shimura, 1990;Simmons et al, 1995;Mullen et al, 1998;Rutherford et al, 1998;Gibson, 2000;Buer et al, 2003;Hobe et al, 2003;Pandey et al, 2008;Chen et al, 2009). The cytoskeleton plays a crucial role in optimal root architecture, as is evident by the root phenotypes of seedlings (Fig.…”

“…Root coiling on a hard surface is an estimate of the spiral-downward root pattern in the soil (Okada and Shimura, 1990;Garbers et al, 1996;Legué et al, 1997;Sack, 1997;Blancaflor et al, 1998;Luschnig et al, 1998;Rutherford et al, 1998;Marchant et al, 1999;Fasano et al, 2001;Rashotte et al, 2001;Gilroy, 2003a, 2003b;Piconese et al, 2003;Buer and Muday, 2004;Chen et al, 2009). Arabidopsis root waving is essentially a flattenedspiral growth pattern on a firm agar medium, positioned at an angle of less than 90°with respect to the gravity vector (Okada and Shimura, 1990;Simmons et al, 1995;Mullen et al, 1998;Thompson and Holbrook, 2004).…”

The Microtubule-Associated Protein END BINDING1b, Auxin, and Root Responses to Mechanical Cues

“…Several Arabidopsis mutants that exhibit altered patterns of growth on the surface of agar plates have been identified [6,8,[10][11][12][13][14][15][16][17][18][19][20][21]. to identify quantitative trait loci (QTL) that contribute to root skewing behaviors [19,22].…”