A Mutation in GIANT CHLOROPLAST Encoding a PARC6 Homolog Affects Spikelet Fertility in Rice

Abstract

Chloroplasts are not generated de novo but proliferate from a pre-existing population of plastids present in meristematic cells. Chloroplast division is executed by the co-ordinated action of at least two molecular machineries: internal machinery located on the stromal side of the inner envelope membrane and external machinery located on the cytosolic side of the outer envelope membrane. To date, molecular studies of chloroplast division in higher plants have been limited to several species such as Arabidopsis. To elucidate chloroplast division in rice, we performed forward genetics and isolated a mutant displaying large chloroplasts among an ethyl methanesulfonate (EMS)-mutagenized Oryza sativa spp japonica Nipponbare population. Using a map-based approach, this mutation, termed giant chloroplast (gic), was allocated in a gene that encodes a protein that is homologous to Paralog of ARC6 (PARC6), which is known to play a role in chloroplast division. GIC is unique in that it has a long C-terminal extension that is not present in other PARC6 homologs. Characterization of gic phenotypes in a rice field showed that gic exhibited defective growth in seed setting, suggesting that the gic mutant negatively affects the reproductive stage. This report is the first describing a chloroplast division mutant in monocotyledons and its effect on plant development.

Amyloplast Membrane Protein SUBSTANDARD STARCH GRAIN6 Controls Starch Grain Size in Rice Endosperm

“…Chloroplast size is controlled by the chloroplast binary fission division machinery, especially by the ring structures at the division sites (Miyagishima, 2011). Rice mutants defective in the ring structures develop enlarged and dumbbellshaped chloroplasts in leaves, but they do not develop enlarged amyloplasts (Yun and Kawagoe, 2009;Kamau et al, 2015). Therefore, ssg4 and ssg6 mutants are unique in that they affect both chloroplasts and amyloplasts.…”

Maize defective kernel5 is a bacterial TamB homologue required for chloroplast envelope biogenesis

“…The more spherical shape and increased volume of dek5 chloroplasts is not commonly reported in chloroplast division mutants. TEM analyses of division mutants show filamentous or buckled chloroplasts with a relatively normal short axis ( Itoh et al, 2001 ; Ii and Webber, 2005 ; Karamoko et al, 2011 ; Kamau et al, 2015 ). Filamentous chloroplasts with a constant short axis can be roughly modeled as a cylinder, and surface area increases linearly with increased volume instead of the nonlinear relationship for ellipsoid-like dek5 chloroplasts ( Fig.…”

Genetic analysis and fine-mapping of a new rice mutant, white and lesion mimic leaf1

“…The yss1 mutant develops striated leaves at the seedling stage, but no abnormal phenotype in leaf 5 and onwards (Zhou et al 2017). GIC encodes a PARC6 homolog, and the gic mutant has fewer and enlarged chloroplasts (Kamau et al 2015). WSL1 encodes a multiple organellar RNA editing factor, and wsp1 mutants exhibit green and white sectors starting from the three-leaf stage and not entirely green panicles at the heading stage .…”