No description available.

Carnation Italian ringspot virus (CIRV) is a positive-strand RNA virus that assembles its membrane-bound replication complexes at mitochondria in plant cells. This process is accompanied by extensive inward invagination of the mitochondrial outer membrane, leading to the formation of cytosol-filled spherules, wherein viral RNA synthesis occurs. The mechanism by which CIRV is able to induce spherule formation is unknown, however growing evidence suggests that the host-cell ESCRT (Endosomal Sorting Complex Required for Transport) machinery – a multi-protein complex normally involved in late endosome maturation – may be involved. ESCRT consists of ~30 soluble proteins that form sub-complexes assembled at the late endosomal surface, and function in multivesicular body (MVB) biogenesis. While ESCRT is relatively well characterized in yeasts and mammals, comparably little is known about ESCRT in plants. Hence, as an initial step towards understanding the potential role of ESCRT in CIRV replication, we examined the protein-protein interaction network, subcellular localization, and gene expression profiles of the Arabidopsis thaliana ESCRT components. Overall, the results from these studies suggest that ESCRT organization and function is relatively well conserved in plants compared to other eukaryotes. We also observed that ESCRT is important for CIRV replication, as expression of dominant-negative versions of several key ESCRT components reduced CIRV replication efficiency in plant cells. Moreover, the Arabidopsis ESCRT-I component, Vps23A is recruited from late endosomes to mitochondria in plant cells expressing the CIRV replicase protein, p36, and recruitment of Vps23A was shown to be mediated by sequences located at the N terminus of p36. It was also shown that recruitment of Vp23A to mitochondria by p36 does not require the Ubiquitin E2 Variant domain of Vps23A, which is in contrast to recruitment of ESCRT by retroviruses during viral budding in mammalian cells. Taken together, these results support the hypothesis that CIRV recruits ESCRT by a novel mechanism in order to carry out its replication, a finding that may lend important insight to aspects of normal ESCRT function in plants.

No description available.

In angiosperms, specialized reproductive structures are borne in flowers to ensure their reproductive success. After the vegetative growth, plants undergo reproductive phase change to produce flowers. Floral meristems (FMs) are generated on the flanks of inflorescence and groups of specialized stem cells in the FM differentiate into four whorls of organs of a flower. In dicots, floral meristem successively gives rise to sepals, petals, stamens and carpels; after which it terminates. The fate of organs formed on FM is under the control of genetic regulators, key among which are members of MADS box transcription factor family. Their individual and combined act confers distinct identities to floral organs. Grass flowers are highly modified in structure. Rice flower, a model for grasses, is borne on a short branch called spikelet and they together from the basic structural units of the rice infloresences known as panicle. The outer whorl organs of a grass floret are bract-like structures known as lemma and palea to dicot sepals is highly dibated (see Chapter 1). In grass florets, petal homologs are a pair of highly reduced, fleshy bracts known as lodicules, while stamen and carpel homologs occupy the same position and share the same functions as their dicot counterparts. Aside from these distinct outer whorl organs, the florets are subtended by two pairs of bracts known as empty glumes and rudimentary glumes. The genetic regulators that control their unique identities and those that perform conserved functions are very intriguing and central questions in plant developmental biology. Using various contemporary and complementary technologies, we have analysed the molecular functions and downstream pathways of a MADS box transcription factor, OsMADSI during the rice floret meristem specification and organ development. Further by reverse genetics and overexpression studies, we have also functionally characterized two target genes of OsMADSI, OsETTINI and OsETTINI2 to understand their roles downstream to OsMADSI during the rice floret development.