Thummala Chandrasekhar

RecX protein abrogates ATP hydrolysis and strand exchange promoted by RecA: Insights into negative regulation of homologous recombination

In many eubacteria, coexpression of recX with recA is essential for attenuation of the deleterious effects of recA overexpression; however, the molecular mechanism has remained enigmatic. Here, we show that Mycobacterium tuberculosis RecX binds directly to M. tuberculosis RecA as well as M. smegmatis and E. coli RecA proteins in vivo and in vitro, but not single-stranded DNA binding protein. The direct association of RecX with RecA failed to regulate the specificity or extent of binding of RecA either to DNA or ATP, ligands that are central to activation of its functions. Significantly, RecX severely impeded ATP hydrolysis and the generation of heteroduplex DNA promoted by homologous, as well as heterologous, RecA proteins. These findings reveal a mode of negative regulation of RecA, and imply that RecX might act as an anti-recombinase to quell inappropriate recombinational repair during normal DNA metabolism.

Research Article : Production of Multiple Shoots and Plant Regeneration from Leaf Segments of Fig Tree (Ficus carica L.)

High frequency of multiple shoots and plant regeneration has been obtained from the leaf segments of fig tree (Ficus carica L.). Budbreak from dormant buds is highly dependent upon cultivar, so we chose cv. Seungjung Dauphine because it shows an excellent degree of budbreak. Tissue-browning can be an important limiting factor duringin vitro culture. This phenomenon could be substantially delayed or reduced by treating the tissues with 0.5 mM phloroglucinol, thus oxidizing the phenolic substances exuded from the segments. Wounded leaf explants cultured on MS medium supplemented with TDZ in combination with IBA produced more multiple shoots than did other combinations of auxin and cytokinin. For example, 2 mg L-1 IBA along with either 0.5 or 1.0 mg L-1 TDZ resulted in 8.1 or 10.8 multiple shoots per explant, respectively. We achieved a frequency of approximately 90% when tissues were first maintained under darkness in the culture medium for one week before being transferred to the light. Regenerated shoots rooted best in a full-strength MS basal medium.In vitro regenerated plant-lets were then successfully transferred to greenhouse conditions. Here, we have demonstrated a regeneration protocol that is suitable for use in conservation as well as genetic transformation studies of figs and related species.

In vitro Micropropagation of Boswellia ovalifoliolata

A protocol for micropropagation of Boswellia ovalifoliolata Bal & Henry (Burseraceae) was developed using cotyledonary nodal explant on Murashige and Skoog modified medium (MS). A comparative study of micropropagation with 6-benzyladenine, kinetin and thidiazuron along with 1-naphthalene acetic acid (0.054 μм) was conducted. The highest shoot multiplication (7.1 ± 0.2 shoots per node) was achieved in 50 d on MS supplemented with thidiazuron (2.72 μм). Excised shoot cuttings of 3.0 cm were placed on the MS basal medium supplemented with indole-3-acetic acid and indole-3-butyric acid alone and in combinations for rooting. Activated charcoal (100 mg l-1) and polyvinylpyrrolidone (40 mg l-1) were added to the medium to prevent browning of cultures. The regenerated plantlets have been successfully acclimatized and transferred to soil.

MACROPHYLLA/ROTUNDIFOLIA3 gene of Arabidopsis controls leaf index during leaf development

In plants, heteroblasty reflects the morphological adaptation during leaf development according to the external environmental condition and affects the final shape and size of organ. Among parameters displaying heteroblasty, leaf index is an important and typical one to represent the shape and size of simple leaves. Leaf index factor is eventually determined by cell proliferation and cell expansion in leaf blades. Although several regulators and their mechanisms controlling the cell division and cell expansion in leaf development have been studied, it does not fully provide a blueprint of organ formation and morphogenesis during environmental changes. To investigate genes and their mechanisms controlling leaf index during leaf development, we carried out molecular-genetic and physiological experiments using an Arabidopsis mutant. In this study, we identified macrophylla (mac) which had enlarged leaves. In detail, the mac mutant showed alteration in leaf index and cell expansion in direction of width and length, resulting in not only modification of leaf shape but also disruption of heteroblasty. Molecular-genetic studies indicated that mac mutant had point mutation in ROTUDJFOLIA3 (ROT3) gene involved in brassinosteroid biosynthesis and was an allele of rod-I mutant. We named it rnac/rot3-5 mutant. The expression of ROT3 gene was controlled by negative feedback inhibition by the treatment of brassinosteroid hormone, suggesting that ROT3 gene was involved in brassinosteroid biosynthesis. in dark condition, in addition, the expression of ROT3 gene was up-regulated and mac/rot3-5 mutant showed lower response, compare to wild type in petiole elongation. This study suggests that ROT3 gene has an important role in control of leaf index during leaf expansion process for proper environmental adaptation, such as shade avoidance syndrome, via the control of brassinosteroid biosynthesis.