Radiation-induced in vitro mutagenesis system for salt tolerance and other agronomic characters in sugarcane(Saccharum officinarum L.)

Gamma ray-induced in vitro mutagenesis and selection for salt(NaC l) tolerance were investigated in sugarcane(Saccharum officinarum L.). Embryogenic callus cultures were irradiated(10 to 80 Gy) and subjected to in vitro selection by exposure of irradiated callus to NaC l(0, 50, 100,150, 200, and 250 mmol L-1). Increasing NaC l concentrations resulted in growth reduction and increased membrane damage. Salt-selected callus lines were characterized by the accumulation of proline, glycine betaine, and Na+and K+concentration. Higher accumulation of proline and glycine betaine was observed in NaC l stressed callus irradiated at 20 Gy. Na+concentration increased and K+concentration decreased with increasing salt level. Irradiated callus showed50–60% regeneration under NaC l stress, and in vitro-regenerated plants were acclimatized in the greenhouse, with 80–85% survival. A total of 138 irradiated and salt-selected selections were grown to maturity and their agronomic performance was evaluated under normal and saline conditions. Of these, 18 mutant clones were characterized for different agro-morphological characters and some of the mutant clones exhibited improved sugar yield with increased Brix%,number of millable canes, and yield. The result suggest that radiation-induced mutagenesis offers an effective way to enhance genetic variation in sugarcane.

Distinct Role of Core Promoter Architecture in Regulation of Light-Mediated Responses in Plant Genes

In the present study, we selected four distinct classes of light-regulated promoters. The light-regulated promoters can be distinctly grouped into either TATA-box-containing or TATA-less （initiator-containing） promoters. Further, using either native promoters or their swapped versions of core promoter elements, we established that TATA-box and Inr （Initiator） elements have distinct mechanisms which are involved in light-mediated regulation, and these elements are not swappable. We identified that mutations in either functional TATA-box or Inr elements lead to the formation of nucleosomal structure. The nucleotide diversity in either the TATA-box or Inr element in Arabidopsis ecotypes proposes that the nucleotide variation in core promoters can alter the gene expression. We show that motif overrepresentation in light-activated promoters encompasses different specific regulatory motifs present downstream of TSS （transcription start site）, and this might serve as a key factor in regulating light promoters which are parallel with these elements. Finally, we conclude that the TATA-box or Inr element does not act in isolation, but our results clearly suggests the probable involvement of other distinct core promoter elements in concurrence with the TATA-box or Inr element to impart selectivity to light-mediated transcription.