rgf1, a mutation reducing grain filling in maize through effects on basal endosperm and pedicel development^†

Abstract

SummaryThe maize cob presents an excellent opportunity to screen visually for mutations affecting assimilate partitioning in the developing kernel. We have identi®ed a defective kernel mutant termed rgf1, reduced grain ®lling, with a ®nal grain weight 30% of the wild type. In contrast with most defective endosperm mutants, rgf1 shows gene dosage-dependent expression in the endosperm. rgf1 kernels possess a small endosperm incompletely ®lling the papery pericarp, but embryo development is unaffected and the seeds are viable. The mutation conditions defective pedicel development and greatly reduces expression of endosperm transfer layer-speci®c markers. rgf1 exhibits striking morphological similarities to the mn1 mutant, but maps to a locus approximately 4 cM away from mn1 on chromosome 2 of maize. Despite reduced starch accumulation in the mutant, no obvious lesion in starch biosynthesis has been detected. Free sugar levels are unaltered in rgf1 endosperm. Rates of sugar uptake, measured over short (8 h) periods in cultured kernels, are increased in rgf1 compared to the wild type. rgf1 and wild-type kernels, excised at 5 DAP and cultured in vitro also develop differently in response to variations in sugar regime: glucose concentrations above 1% arrest placentochalazal development of rgf1 kernels, but have no effect on cultured wild-type kernels. These ®ndings suggest that either uptake or perception of sugar(s) in endosperm cells at 5±10 DAP determines the rgf1 kernel phenotype.

Maternal Gametophytic baseless1 Is Required for Development of the Central Cell and Early Endosperm Patterning in Maize (Zea mays)

“…Because the BETL is the primary site for the transfer of solutes from the mother plant to the seed (Thompson et al 2001), an impaired BETL would produce significant changes to nutrient influx, resulting in pleiotropic effects on seed development. This phenomenon has been observed in other zygotic mutants possessing a defective BETL (Cheng et al 1996;Maitz et al 2000;Costa et al 2003) and in maternal-effect mutants with defective connecting maternal sporophytic tissue (Felker et al 1985). Moreover, an impaired BETL would certainly account for the slower growth and delayed programmed cell death in bsl1 kernels when compared to wild-type siblings (data not shown).…”

“…Moreover, an impaired BETL would certainly account for the slower growth and delayed programmed cell death in bsl1 kernels when compared to wild-type siblings (data not shown). Similar to reduced grain filling1 mutants in maize (Maitz et al 2000), expression of BETL-specific genes was downregulated in bsl1 mutants, although BETL-specific transcripts were often confined to discrete portions of the adgerminal and abgerminal basal endosperm. Although we are currently uncertain of the direct effects of the bsl1 mutation on embryo development, it is likely that the retarded growth of bsl1/1 embryos is caused by the inability of compromised bsl1/bsl1/1 endosperms to support their growth.…”

Arabidopsis haiku Mutants Reveal New Controls of Seed Size by Endosperm

“…Transfer of nutrients from the mother plant to the endosperm that stores reserves involves the specialized placentochalazal tissue of seed integument and the transfer layer in the endosperm (Thompson et al, 2001). Mutants affected for the development of the placentochalazal tissue show defects in seed growth (Felker et al, 1985;Cheng et al, 1996;Maitz et al, 2000). Most of these mutants have sporophytic maternal effects on endosperm and embryo development.…”

MaizeRough Endosperm3Encodes an RNA Splicing Factor Required for Endosperm Cell Differentiation and Has a Nonautonomous Effect on Embryo Development

“…Developing maize kernels transport nutrients from the maternal plant through the basal endosperm transfer cell layer (BETL), and prior reports of reduced grain fill mutations suggest that defects in transfer cells are associated with reduced seed size (Lowe and Nelson, 1946;Brink and Cooper, 1947;Maitz et al, 2000;Costa et al, 2003;Gutié rrez-Marcos et al, 2007). We analyzed sections stained with toluidine blue for BETL morphological defects.…”