GROWTH RESPONSES OF ARABIDOPSIS DNA REPAIR MUTANTS TO SOLAR RADIATION.

Authors: BRITT, ANNE - UNIVERSITY OF CAL. DAVIS; Fiscus, Edwin

Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/12/2002
Publication Date: 6/12/2003
Citation: Britt, A.B., Fiscus, E.L. 2003. Growth responses of Arabidopsis DNA repair mutants to solar radiation. Physiologia Plantarum 118:183-192.

Interpretive Summary: Plants are subject to a variety of environmental challenges including damage to their genetic code (DNA) by normal solar ultraviolet radiation. High-energy UV-B radiation can cause a variety of direct damage to plant DNA which may cause interference with the process of reading the genetic code or may change the code itself. Plants and animals have evolved numerous mechanisms for detecting and repairing such damage. Some of these are rapid and very specific to particular types of damage and interestingly, require light in order to function properly; these are called photolyases. Other, much slower mechanisms exist which are not light dependent, but which can repair a much wider variety of damage products. Many mutations have been isolated in the plant Arabidopsis which are deficient in specific repair mechanisms. These mutations are generally grown and their effects assessed under laboratory conditions, but a more complete understanding of their significance requires that they be assesse under normal solar radiation, and that is what we are doing. Not surprisingly, we found that the mutation lacking the photolyase responsible for repairing the most common type of UV damage appeared to be the most sensitive to UV-B. The presence of the next most important photolyase seemed not to make a difference and the absence of the dark repair mechanisms, although conferring a small additional degree of sensitivity by itself seemed to act in a protective manner when combined with the other mutations. We are uncertain whether the minimal effect of the absence of the dark repair mechanisms and the second most important photolyase may have been due to the levels of damage relevant to those mechanisms or the plants ability to more easily tolerate those particular types of damage.

Technical Abstract: Four Arabidopsis DNA-repair mutants deficient in generalized dark repair (uvr1), photorepair of CPDs (uvr2) and photorepair of 6-4 products (uvr3) and combinations of the mutants, along with the wild type Ler were grown in outdoor temperature-controlled chambers which admit the full range of UV and visible radiation, in an attempt to evaluate the relative significance of these various repair mechanisms under conditions approaching a natural environment. We found that, under our conditions, all lines, including the repair-proficient progenitor Landsberg erecta, displayed significant inhibition of growth when exposed to the UV-B component of sunlight. Eliminating the dark repair (UVR1-dependent) pathway for the removal of UV-induced photoproducts increases somewhat this sensitivity to UV-B, suggesting that this generalized pathway plays a relatively minor role in UV-resistance in Arabidopsis. In contrast, mutants defective in the UVR2-encoded CPD-specific photolyase displayed much higher sensitivity to growth inhibition by natural levels of UV-B than their repair-proficient progenitor line, indicating that this specialized repair pathway is more critical for optimal plant growth under natural light. Somewhat surprisingly, the presence of a functional UVR3 gene, which encodes a photolyase specific for pyrimidine [6-4]pyrimidinone dimers, did not have detectable effect on the growth of mature Arabidopsis plants under our experimental regime.