Abstract
BackgroundPhytyl residues are the common side chains of chlorophyll (Chl) and tocopherols. Geranylgeranyl reductase (GGR), which is encoded by CHLP gene, is responsible for phytyl biosynthesis. The light-harvesting like protein LIL3 was suggested to be required for stability of GGR and protochlorophyllide oxidoreductase in Arabidopsis.ResultsIn this study, we isolated a yellow-green leaf mutant, 637ys, in rice (Oryza sativa). The mutant accumulated majority of Chls with unsaturated geranylgeraniol side chains and displayed a yellow-green leaf phenotype through the whole growth period. The development of chloroplasts was suppressed, and the major agronomic traits, especially No. of productive panicles per plant and of spikelets per panicle, dramatically decreased in 637ys. Besides, the mutant exhibited to be sensitive to light intensity and deficiency of tocopherols without obvious alteration in tocotrienols in leaves and grains. Map-based cloning and complementation experiment demonstrated that a point mutation on the OsLIL3 gene accounted for the mutant phenotype of 637ys. OsLIL3 is mainly expressed in green tissues, and its encoded protein is targeted to the chloroplast. Furthermore, the 637ys 502ys (lil3 chlp) double mutant exclusively accumulated geranylgeranyl Chl and exhibited lethality at the three-leaf stage.ConclusionsWe identified the OsLIL3 gene through a map-based cloning approach. Meanwhile, we demonstrated that OsLIL3 is of extreme importance to the function of OsGGR, and that the complete replacement of phytyl side chain of chlorophyll by geranylgeranyl chain could be fatal to plant survival in rice.
Highlights
Phytyl residues are the common side chains of chlorophyll (Chl) and tocopherols
OsLIL3 is mainly expressed in green tissues and its encoded protein is localized to the chloroplast
We found a gene, LOC_Os02g03330, which encodes a light-harvesting like protein with 57 and 58% identities to LIL3:1 and LIL3:2 in Arabidopsis respectively (Fig. 6d)
Summary
Phytyl residues are the common side chains of chlorophyll (Chl) and tocopherols. The light-harvesting like protein LIL3 was suggested to be required for stability of GGR and protochlorophyllide oxidoreductase in Arabidopsis. Vitamin E, including tocopherols and tocotrienols, is a potent antioxidant, and is generally believed to arise from the condensation of homogentisic acid (HGA) and phytyl-PP or geranylgeranyl diphosphate (GGPP). Chls and tocopherols harbor a common phytyl residue. Many LIL proteins have been identified in land plants and green algae as well as in cyanobacteria, including single-helix proteins (OHPs), known as high-light induced proteins (HLIPs), double-helix stress-enhanced proteins (SEPs), three-helix early lightinduced proteins (ELIPs), and four-helix PsbS protein [18, 20,21,22,23,24,25,26,27,28]. LIL3:1 and LIL3:2 contribute to regulating Chl and tocopherol biosynthesis [18, 20]
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