Arabidopsis dwarf

Some biochemical functions defined by the Arabidopsis dwarf mutants were later confirmed by heterologous expression of genes and by in vivo conversion of postulated substrates [17-20]. As part of these physiological and biochemical studies, tomato cell suspension cultures have also been established to investigate intermediates and enzymes of brassinosteroid biosynthesis and metabolism [21-23]. Enzyme activities from partially purified protein extracts were first detected in this model system [24]. 

Another dwarf mutant of Arabidopsis, sax], defines a step upstream of DWF1 in the brassinosteroid biosynthesis pathway [27]. Rescue experiments with intermediates showed that saxl is involved in the oxidation and isomerization of 3P-hydroxyl,A5 6 precursors to 3-oxo-A4 5 steroids (Fig. (4)). 

The dwarf mutants of Arabidopsis show, when grown in the dark, many of the characteristics of light-grown plants, including cotyledon expansion, primary leaf initiation, anthocyanin accumulation, and depression of light-regulated gene expression. Involvement of BR in de-etiolation has been discussed.816... 

Fig. 9. Increased stearic acid causes severe dwarfing of Arabidopsis [28]. A wild-type Arabidopsis plant (left) is compared to the f>2 mutant (right) in which leaf stearic acid content has increased from 1 to 14%. Photo courtesy of John Browse, Washington State University.

The dwarf mutants of pea (Ikb) [34] and Arabidopsis dim) [35,36] accumulate 24-methylenecholesterol and isofucosterol and are deficient in campesterol and sitosterol. In the Ikb mutant, the levels of endogenous BRs are significantly reduced. Thus, blocked synthesis of campesterol causes dwarfism by reducing the level of endogenous BRs (Eig. 2). 

Overall, epimerization of the 3a-hydroxyl and/or introduction of a hydroxyl group at C25 and C26 is critical for the metabolism of 24-epicastasterone and 24-epibrassinolide in tomato cells. In the rice lamina inclination assay, 25-hydroxy-24-epibrassinolide is tenfold more active than 24-epibrassinolide, but 26-hydroxy-24-epibrassinolide is less active. However, 25-hydroxy-24-epibrassinolide is hundred-fold less active in restoring the dwarf phenotype of the BR-deficient Arabidopsis mutants [72], Therefore, although the... 

Many studies of the molecular mechanisms of plant growth have been performed using genetic methods in Arabidopsis. In the past decade, the identihcation and characterization of Arabidopsis B R biosynthetic mutants such as det2 and dw[4 has revealed the importance of BRs in plant growth regulation. These BR-dehcient mutants have a pleiotropic dwarf phenotype that can be reverted to a wild-type-like phenotype by feeding with BL. 

Takahashi N, Nakazawa M, Shibata K, Yokota T, Ishikawa A, Suzuki K, Kawashima M, Ichikawa T, Shimada H, Matsui M (2005b) shkl-D, a dwarf Arabidopsis mutant caused by activation of the CYP72C1 gene, has altered brassinosteroid levels. Plant J 42 13-22... 

His I., Driouich A., Nicol F., Jauneau A., and Hofte H. 2001. Altered pectin composition in primary cell walls of korrigan, a dwarf mutant of Arabidopsis deficient in a membrane-bound endo-1, 4-beta-glucanase. Planta 212(3) 348-358. 

Nandi, A., KrothapaUi, K., Buseman, C.M., Li, M., Welti, R., Enyedi, A. and Shah, J. (2003) Arabidopsis sfd mutants affect plastidic Upid composition and suppress dwarfing, cell death, and the enhanced disease resistance phenotypes resulting from the deficiency of a fatty acid desaturase. Plant Cell 15, 2383-2398. 

Fig. 3.4 Foity-day-old plants of the wild type (Col-0) and bud2, bud2 sac5I-d, and bud2 sac52-d mutants of Arabidopsis The semi-dwarf phenotype of bud2, a knockout mutant of SAMDC4, is suppressed by dominant suppressors of acl5, sac51-d and sac52-d...

Imai A, Hanzawa Y, Komura M, Yamamoto KT, KomedaY, Takahashi T (2006) The dwarf phenotype of the Arabidopsis acl5 mutant is suppressed by a mutation in an upstream ORF of a bHLH gene. Development (Camb) 133 3575-3585 Imai A, Komura M, Kawano E, Kuwashiro Y, Takahashi T (2008) A semi-dominant mutation in the ribosomal protein LIO gene suppresses the dwarf phenotype of the acl5 mutant in Arabidopsis thaliana. Plant J 56 881-890... 

Imai A, Hanzawa Y, Komura M et til (2006) The dwarf phenotype of the Arabidopsis acl5 mutant is suppressed by a mutation in an upstream ORF of a bHLH gene. Development (Ctunb) 133 3575-3585... 

---