The isolation and characterization of mutants hypersensitive to ultraviolet (UV) radiation has been a powerful tool to learn about the mechanisms that protect plants against UV-induced damage. To increase our understanding of the various mechanisms of defense against UVB radiation, we searched for mutations that would increase the level of tolerance of Arabidopsis plants to UV radiation. We describe a single gene dominant mutation (uvt1) that leads to a remarkable tolerance to UVB radiation conditions that would kill wild-type plants. Pigment analyses show a constitutive increase in accumulation of UV-absorbing compounds in uvt1 that increases the capacity of the leaves to block UVB radiation and therefore is likely to be responsible for the elevated resistance of this mutant to UVB radiation. These increases in absorption in the UV region are due, at least in part, to increases in flavonoid and sinapate accumulation. Expression of chalcone synthase (CHS) mRNA was shown to be constitutively elevated in uvt1 plants, suggesting that the increases in absorption may be a consequence of changes in gene expression. Expression of CHS in uvt1 was shown to be still inducible by UV, indicating that the uvt1 lesion may not affect the UV-mediated regulation of CHS gene expression. Our data support an important role for UV screens in the overall protection of plants to UVB radiation. The uvt1 mutant could prove to be an important tool to elucidate further the exact role of UV-absorbing pigments in UV protection as well as the relative contribution of other mechanisms to the overall tolerance of plants to UV radiation.

译文

对紫外线 (UV) 辐射敏感的突变体的分离和表征已成为了解保护植物免受紫外线诱导的损害的机制的有力工具。为了加深我们对防御UVB辐射的各种机制的了解,我们寻找了可以提高拟南芥植物对紫外线辐射耐受性水平的突变。我们描述了一个单基因显性突变 (uvt1),该突变导致对UVB辐射条件的显着耐受性,从而杀死野生型植物。色素分析表明,uvt1中吸收紫外线的化合物的积累增加,从而增加了叶片阻挡UVB辐射的能力,因此很可能是该突变体对UVB辐射的抗性提高的原因。紫外线区域吸收的这些增加至少部分是由于类黄酮和芥子酸积累的增加。在uvt1植物中,查尔酮合酶 (CHS) mRNA的表达呈组成性升高,这表明吸收的增加可能是基因表达变化的结果。UV仍可诱导CHS在uvt1中的表达,表明uvt1病变可能不影响UV介导的CHS基因表达调控。我们的数据支持紫外线筛选在植物对UVB辐射的整体保护中发挥重要作用。uvt1突变体可能被证明是进一步阐明吸收紫外线的颜料在紫外线防护中的确切作用以及其他机制对植物对紫外线辐射的总体耐受性的相对贡献的重要工具。

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