A deficiency of coproporphyrinogen III oxidase causes lesion formation in Arabidopsis

Abstract

SummaryWe isolated an Arabidopsis lesion initiation 2 (lin2) mutant, which develops lesion formation on leaves and siliques in a developmentally regulated and light-dependent manner. The phenotype of the lin2 plants resulted from a single nuclear recessive mutation, and LIN2 was isolated by a T-DNA tagging approach. LIN2 encodes coproporphyrinogen III oxidase, a key enzyme in the biosynthetic pathway of chlorophyll and heme, a tetrapyrrole pathway, in Arabidopsis. The lin2 plants express cytological and molecular markers associated with the defense responses, usually activated by pathogen infection. These results demonstrate that a porphyrin pathway impairment is responsible for the lesion initiation phenotype, which leads to the activation of defense responses, in Arabidopsis. Lesion formation was not suppressed, and was even enhanced when accumulation of salicylic acid (SA) was prevented in lin2 plants by the expression of an SA-degrading salicylate hydroxylase (nahG) gene. This suggests that the lesion formation triggered in lin2 plants is determined prior to or independently of the accumulation of SA but that the accumulation is required to limit the spread of lesions in lin2 plants.

The Oligomeric Stromal Proteome of Arabidopsis thaliana Chloroplasts

“…Together they totaled about 0.5% of the stromal protein mass. Porphobilinogen synthase (At1g69740; ϳ45 kDa) and coproporphyrinogen III oxidase (At103475; ϳ40 kDa) were reported to form a homooctamer (24) and a homodimer (71). We identified each on the CN-PAGE gel at ϳ340 and 82 kDa, which corresponds to these reported oligomeric states.…”

Reactive oxygen species generation and signaling in plants

“…84,85 The Arabidopsis coproporphyrinogen oxidase mutants (lin2; lesion initiation 2) had pale leaves and developed lesions on the young leaves. 83 3,3-Diamino benzidine and trypan blue staining of the mutant leaves shows H 2 O 2 accumulation and cell death. Seedlings homozygous for a null mutation in the cpx1 gene of maize completely lack chlorophyll and develop necrotic lesions in the light.…”

“…80 Coll et al 81 82 Apart from Pchlide, early intermediates i.e., coproporphyrin also acts as a photosensitizer. [83][84][85] The antisense coproporphyrinogen oxidase (that converts coproporphyrinogen III to protoporphyrinogen IX) in tobacco plants, have an excessive amount of coproporphyrin. This oxidized porphyrin gives rise to photodynamic reactions, which affect cellular processes resulting in retarded growth and necrotic leaves.…”

Tetrapyrrole Metabolism Is Involved in Lesion Formation, Cell Death, in theArabidopsis lesion initiation 1Mutant

“…len1 and lin2 were described previously. 6,20) cs was a gift from Dr. Mochizuki. hy1 and hy2 were gifts from Dr. Kohchi.…”