Mutant

About: Mutant is a research topic. Over the lifetime, 74520 publications have been published within this topic receiving 3477079 citations.

The AUXIN RESPONSE FACTOR 2 gene of Arabidopsis links auxin signalling, cell division, and the size of seeds and other organs

Abstract: Control of seed size involves complex interactions among the zygotic embryo and endosperm, the maternally derived seed coat, and the parent plant. Here we describe a mutant in Arabidopsis, megaintegumenta (mnt), in which seed size and weight are dramatically increased. One factor in this is extra cell division in the integuments surrounding mnt mutant ovules, leading to the formation of enlarged seed coats. Unusually for integument mutants, mnt does not impair female fertility. The mnt lesion also has pleiotropic effects on vegetative and floral development, causing extra cell division and expansion in many organs. mnt was identified as a mutant allele of AUXIN RESPONSE FACTOR 2 (ARF2), a member of a family of transcription factors that mediate gene expression in response to auxin. The mutant phenotype and gene expression studies described here provide evidence that MNT/ARF2 is a repressor of cell division and organ growth. The mutant phenotype also illustrates the importance of growth of the ovule before fertilization in determining final size of the seed.

Regulation of carotenoid biosynthesis during tomato fruit development: expression of the gene for lycopene epsilon-cyclase is down-regulated during ripening and is elevated in the mutant Delta.

Abstract: The red colour of tomato (Lycopersicon esculentum) fruits is provided by the carotenoid pigment lycopene whose concentration increases dramatically during the ripening process. A single dominant gene, Del, in the tomato mutant Delta changes the fruit colour to orange as a result of accumulation of delta-carotene at the expense of lycopene. The cDNA for lycopene epsilon-cyclase (CrtL-e), which converts lycopene to delta-carotene, was cloned from tomato. The primary structure of CRTL-E is 71% identical to the homologous polypeptide from Arabidopsis and 36% identical to the tomato lycopene beta-cyclase, CRTL-B. The CrtL-e gene was mapped to a single locus on chromosome 12 of the tomato linkage map. This locus co-segregated with the Del gene. In the wild-type tomato, the transcript level of CrtL-e decreases at the 'breaker' stage of ripening to a non-detectable level in the ripe fruit. In contrast, it increases approximately 30-fold during fruit ripening in the Delta plants. The Delta mutation does not affect carotenoid composition nor the mRNA level of CrtL-e in leaves and flowers. These results strongly suggest that the mutation Del is an allele of the gene for epsilon-cyclase. Together with previous data, our results indicate that the primary mechanism that controls lycopene accumulation in tomato fruits is based on the differential regulation of expression of carotenoid biosynthesis genes. During fruit development, the mRNA levels for the lycopene-producing enzymes phytoene synthase (PSY) and phytoene desaturase (PDS) increase, while the mRNA levels of the genes for the lycopene beta- and epsilon-cyclases, which convert lycopene to either beta- or delta-carotene, respectively, decline and completely disappear.

A plasma membrane‐bound putative endo‐1,4‐β‐D‐glucanase is required for normal wall assembly and cell elongation in Arabidopsis

Abstract: Endo‐1,4‐β‐d‐glucanases (EGases) form a large family of hydrolytic enzymes in prokaryotes and eukaryotes. In higher plants, potential substrates in vivo are xyloglucan and non‐crystalline cellulose in the cell wall. Gene expression patterns suggest a role for EGases in various developmental processes such as leaf abscission, fruit ripening and cell expansion. Using Arabidopsis thaliana genetics, we demonstrate the requirement of a specialized member of the EGase family for the correct assembly of the walls of elongating cells. KORRIGAN ( KOR ) is identified by an extreme dwarf mutant with pronounced architectural alterations in the primary cell wall. The KOR gene was isolated and encodes a membrane‐anchored member of the EGase family, which is highly conserved between mono‐ and dicotyledonous plants. KOR is located primarily in the plasma membrane and presumably acts at the plasma membrane–cell wall interface. KOR mRNA was found in all organs examined, and in the developing dark‐grown hypocotyl, mRNA levels were correlated with rapid cell elongation. Among plant growth factors involved in the control of hypocotyl elongation (auxin, gibberellins and ethylene) none significantly influenced KOR ‐mRNA levels. However, reduced KOR ‐mRNA levels were observed in det2 , a mutant deficient for brassinosteroids. Although the in vivo substrate remains to be determined, the mutant phenotype is consistent with a central role for KOR in the assembly of the cellulose–hemicellulose network in the expanding cell wall.

The Critical Requirement for Linolenic Acid Is Pollen Development, Not Photosynthesis, in an Arabidopsis Mutant.

Abstract: The very high proportions of trienoic fatty acids found in chloroplast membranes of all higher plants suggest that these lipid structures might be essential for photosynthesis. We report here on the production of Arabidopsis triple mutants that contain negligible levels of trienoic fatty acids. Photosynthesis at 22[deg]C was barely affected, and vegetative growth of the mutants was identical with that of the wild type, demonstrating that any requirement for trienoic acyl groups in membrane structure and function is relatively subtle. Although vegetative growth and development were unaffected, the triple mutants are male sterlle and produce no seed under normal conditions. Comparisons of pollen development in wild-type and triple mutant flowers established that pollen grains in the mutant developed to the tricellular stage. Exogenous applications of [alpha]-llnolenate or jasmonate restored fertility. Taken together, the results demonstrate that the critical role of trienoic acids in the life cycle of plants is as the precursor of oxylipin, a signaling compound that regulates final maturation processes and the release of pollen.