Biochemical characteristics of cyclobutane pyrimidine dimer photolyase and UV-B protecting mechanisms of mice (Oryza sativa L.)

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We made several new findings in the period of 2000 and 2002.1:UV-sensitive nice Norin 1 is deficient in photorepair of cyclobutane pyrimidine diners (CPDs). Using a photoflash approach, we showed that the deficiency in photorepair in vivo resulted from a structure/function alteration photolyase. These results were confirmed by studies with extracts, which showed that the Norin 1 photolyase-dimer complex was highly thermolabile relative to the UV-resistant Sasanishiki photolyase.2:CPD photolyase gene from Sasanishiki and Norin 1 were cloned and sequenced. They were found to encode an ORF for 506 amino acid residues. Amino acid at position 126 was glutamine in Sasanishiki, but was arginine in Norin 1.3:GST-fusion rice CPD photolyase was purified from E. coli KY20, and we determined FAD as one of the two chromophores.4:Dark-grown etiolated rice seedlings did hardly have CPD photolyase activity. The induction of CPD photolyase in dark-grown seedlings was under photocontrol of phytochrome, and the expression of photolyase gene was under photocontrol of phytochrome and/or cryptochrome.5:We started to produce a transgenic rice plant into which CPD photolyase gene was transformed using the Agrobacterium transformation system.6:The growth of near-isogenic line (NIL) of rice for purple leaf gene pl of rice with a genetic background of Taichung 65 (T-65) was significantly decreased relative to T-65 in the elevated UV-B during culture regardless of higher accumulation of UV-absorbing compounds and anthocyanins than T-65. The steady-state CPD levels in the NIL was also higher than that in T-65. We showed that the growth stunting and increase in CPD levels under chronic UV-B irradiated with visible light might be due to the difference in the screening effects of UV-B effective for producing CPD levels and blue/UV-A effective for CPD photolyase activity.