https://www.cell.com/trends/plant-science/pdf/S1360-1385(99)01419-3.pdf

A guide to the Lhc genes and their relatives in Arabidopsis

An albino mutant designated cla1-1 (for "cloroplastos alterados', or "altered chloroplasts') has been isolated from a T-DNA-generated library of Arabidopsis thaliana. In cla1-1 plants, chloroplast development is arrested at an early stage. cla1-1 plants behave like wild-type in their capacity to etiolate and produce anthocyanins indicating that the light signal transduction pathway seems to be unaffected. Genetic and molecular analyses show that the disruption of a single gene, CLA1, by the T-DNA insertion is responsible for the mutant phenotype. RNA expression patterns indicate that CLA1 is positively regulated by light and that it has different effects on the steady-state RNA levels of some nuclear- and chloroplast-encoded photosynthetic genes. Although the specific function of the CLA1 gene is still unknown, it encodes a novel protein conserved in evolution between photosynthetic bacteria and plants which is essential for chloroplast development in Arabidopsis.

CLA1, a novel gene required for chloroplast development, is highly conserved in evolution.

In higher plants, the chloroplast NAD(P)H dehydrogenase (NDH) complex mediates photosystem I (PSI) cyclic and chlororespiratory electron transport. We reported previously that NDH interacts with the PSI complex to form a supercomplex (NDH-PSI). In this study, NDH18 and FKBP16-2 (FK506 Binding Protein 16-2), detected in the NDH-PSI supercomplex by mass spectrometry, were shown to be NDH subunits by the analysis of their knockdown lines. On the basis of extensive mutant characterization, we propose a structural model for chloroplast NDH, whereby NDH is divided into four subcomplexes. The subcomplex A and membrane subcomplex are conserved in cyanobacteria, but the subcomplex B and lumen subcomplex are specific to chloroplasts. Two minor light-harvesting complex I proteins, Lhca5 and Lhca6, were required for the full-size NDH-PSI supercomplex formation. Similar to crr pgr5 double mutants that completely lack cyclic electron flow activity around PSI, the lhca6 pgr5 double mutant exhibited a severe defect in growth. Consistent with the impaired NDH activity, photosynthesis was also severely affected in mature leaves of lhca6 pgr5. We conclude that chloroplast NDH became equipped with the novel subcomplexes and became associated with PSI during the evolution of land plants, and this process may have facilitated the efficient operation of NDH.

Efficient Operation of NAD(P)H Dehydrogenase Requires Supercomplex Formation with Photosystem I via Minor LHCI in Arabidopsis

▪ Abstract Cytokinesis in plant cells is more complex than in animals, as it involves building a cell plate as the final step in generating two cells. The cell plate is built in the center of phragmoplast by fusion of Golgi-derived vesicles. This step imposes an architectural problem where ballooning of the fused structures has to be avoided to create a plate instead. This is apparently achieved by squeezing the vesicles into dumbbell-shaped vesicle-tubule-vesicle (VTV) structures with the help of phragmoplastin, a homolog of dynamin. These structures are fused at their ends in a star-shaped body creating a tubulovesicular “honeycomb-like” structure sandwiched between the positive ends of the phragmoplast microtubules. This review summarizes our current understanding of various mechanisms involved in budding-off of Golgi vesicles, delivery and fusion of vesicles to initiate cell plate, and the synthesis of polysaccharides at the forming cell plate. Little is known about the molecular mechanisms involved i...

Cytokinesis and building of the cell plate in plants.

Structure and biogenesis of the chloroplast NAD(P)H dehydrogenase complex

Isolation and expression of an Arabidopsis 14-3-3 like protein gene

Reduced expression of a nuclear gene of Arabidopsis thaliana, Akr, results in the formation of chlorotic plants due to a block in the proplastid-to-chloroplast development pathway (H. Zhang, D.C. Scheirer, W. Fowle, H.M. Goodman [1992] Plant Cell 4: 1575–1588). In an effort to discern the function of the Akr gene product in chloroplast development, transgenic plants containing an Akr::[beta]-glucuronidase gene fusion were constructed to monitor the spatial and temporal patterns of Akr expression. Akr is expressed only in chloroplast-containing tissues and maximal expression occurs during the seedling stage, coincident with chloroplast development. This result is consistent with the hypothesis that Akr is required at an early stage of chloroplast development. The effects of an AKR deficiency on the expression of nuclear and plastid genes required for photosynthetic activity were also examined. Within chloroplast-deficient leaves of plants in which Akr expression is limited by the presence of Akr antisense transgenes or truncated Akr sense transgenes, mRNAs for the nuclear genes Cab2, Cab4, RbcS, and GapA are present at wild-type levels; similarly, levels of mRNAs for the plastid genes rbcL and psbA are not affected by the AKR deficiency. Thus, although expression of these photosynthetic genes is tightly coordinated with the development and maintenance of chloroplasts in wild-type plants, their expression is unaffected in AKR-deficient chlorotic leaves. Therefore, we propose that Akr functions in a pathway different from the one controlling the expression and regulation of the photosynthetic genes during chloroplast development, and at a specific developmental stage after the putative plastid factor is made.

Expression of the Arabidopsis Gene Akr Coincides with Chloroplast Development

A cDNA clone of the gene Lhca2 encoding a photosystem I (PSI) type II chlorophyll a/b-binding protein was isolated from Arabidopsis thaliana. The isolation of this, the fourth PSI cab gene from Arabidopsis, confirms a previous report [1] that indicated Arabidopsis may contain all four PSI cab genes identified in other plant species. Lhca2 is a single-copy gene as are the other known Arabidopsis PSI cab genes. The patterns of developmental expression and tissue-specific regulation of Lhca2 are similar to those of other PSI and PSII cab genes, but the light induction pattern and the steady-state mRNA level of Lhca2 are distinct. This suggests that a different mechanism may be employed to regulate the expression of Lhca2.

Differential expression in Arabidopsis of Lhca2, a PSI cab gene.

Arabidopsis contains one of the smallest angiosperm genomes (Meyerowitz and Pruitt, 1985); however, the polypeptide composition of its light-harvesting complex is as complicated as that of other plants with much larger genomes. For example, McGrath et al. (1992) showed that Arabidopsis may contain a11 the DNA sequences homologous to the different types of cab genes found in tomato. Recently, when we were sequencing an Arabidopsis cDNA clone of a transcriptional activator, we found a cab cDNA linked to its 3' side. Here we present the characterization of this cab cDNA clone, which shows a homology of 79% to a tomato gene, Cab-8. Cab-8 encodes a protein for the third type of cab peptide localized in PSI. According to the nomenclature recommended for cab genes (Jansson et al., 1992), we named this new cab gene Lhca3*l. Arabidopsis Lhca3*l is a single-copy gene, as is the case for Cab-8 in tomato. However, the steady-state level of Lhca3*l mRNA is comparable to those of PSII cab mRNAs in Arabidopsis (data not shown), whereas in tomato the expression of Cab-8 is severalfold lower (Pichersky et al., 1989). Arabidopsis Lhca3*l encodes a protein of 273 amino acids, with a M, of 29,103. Although we have not done S1 mapping or primerextension experiments, the size of the first ORF and the high homology of the protein encoded by the ORF to other PSI type I11 cab proteins suggest that the cDNA sequence reported here is near full length. Severa1 gene bank entries, listed as expressed sequence taqs, are in fact partia1 cDNA sequences derived from Lhca3*l, such as T04458, T04571, and ATTS0425. These expressed sequence taq clones are now maintained at, and can be obtained from, the Arabidopsis Biological Resource Center of Ohio State University, Columbus, OH.

/pdf/an-arabidopsis-cab-gene-homologous-to-cab-8-of-tomato-3k8cyolx8v.pdf

An Arabidopsis Cab Gene Homologous to Cab-8 of Tomato'

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Isolation and expression of an Arabidopsis 14-3-3 like protein gene

Expression of the Arabidopsis Gene Akr Coincides with Chloroplast Development

Differential expression in Arabidopsis of Lhca2, a PSI cab gene.

An Arabidopsis Cab Gene Homologous to Cab-8 of Tomato'