Genomic DNA sequences of two new genes for new storage protein glutelin in rice

Spatial Distribution and Characteristics of Protein Content and Composition in Japonica Rice Grains: Implications for Sake Quality

The quantity and composition of rice proteins play a crucial role in determining taste quality of sake, Japanese rice wine. However, the spatial distribution of proteins within rice grains, especially in endosperm tissue, and the differences between rice varieties remain unclear. Here, we analyzed the crude protein contents and composition ratios of table (Nipponbare and Koshihikari) and genuine sake rice varieties (Yamadanishiki, Gohyakumangoku, Dewasansan, Dewanosato, and Yumenokaori) to elucidate their spatial distribution within the Japonica rice grain endosperm. Seven sake rice varieties were polished over five harvest years using a brewer's rice-polishing machine. We obtained fractions at 90-70% (the outermost endosperm fraction), 70-50%, 50-30%, and 30-0% (the central region of the endosperm fraction). Yamadanishiki and Dewanosato exhibited considerably lower crude protein contents than the other cultivars. After applying SDS-PAGE, the protein composition, comprising glutelin/total protein (G/TP), prolamin/TP (P/TP), and G/P ratios of these fractions was determined. In white rice (at a 90% rice-polishing ratio), the average ratio of the major protein composition was G/TP 41%, P/TP 21%, and G/P ratios of 1.97. Gohyakumangoku and Yamadanishiki had higher G/TP ratio, while Dewanosato had a lower value. Despite having lower crude protein contents, Yamadanishiki and Dewanosato exhibited significantly varying G/TP ratios. The G/TP ratio markedly varied among rice varieties, particularly in the rice grains' central region. The 50-30% fraction had the highest P/TP ratio among all tested rice varieties, suggesting spatial differences in P/TP within rice grains. Koshihikari had the lowest P/TP ratio. In addition, the 50-30% fraction had the lowest G/P ratio among all tested rice varieties, with Gohyakumangoku having the highest G/P ratio. Dewanosato had the lowest G/P value, and this value significantly differed from that of Yamadanishiki in the 30-0% fraction. We found substantial differences in protein composition within distinct spatial regions of rice grains, and larger differences among rice varieties were observed in the rice grain's central region.

Generation of major glutelin-deficient (GluA, GluB, and GluC) semi-dwarf Koshihikari rice line

KEY MESSAGE

We generated a new Koshihikari rice line with a drastically reduced content of glutelin proteins and higher lodging resistance by using new and conventional plant breeding techniques. Using CRISPR/Cas9-mediated genome editing, we generated mutant rice with drastically decreased contents of major glutelins. A Koshihikari rice mutant line, a123, lacking four glutelins (GluA1, GluA2, GluB4, and GluB5) was used as a host, and another five major glutelin genes (GluA3, GluB1a, GluB1b, GluB2, and GluC) were knocked out through two iterations of Agrobacterium-mediated transformation. Mutant seeds were deficient in the GluA family, GluB family, and GluC, and the line obtained was named GluABC KO. Glutelin content was much lower in GluABC KO than in the existing low-glutelin rice mutant LGC-1. A null segregant of GluABC KO was selected using new-generation sequencing and backcrossing, and the sd-1 allele for the semi-dwarf trait was introduced to increase lodging resistance.

Gene Expression in the Developing Seed of Wild and Domesticated Rice

The composition and nutritional properties of rice are the product of the expression of genes in the developing seed. RNA-Seq was used to investigate the level of gene expression at different stages of seed development in domesticated rice (Oryza sativa ssp. japonica var. Nipponbare) and two Australian wild taxa from the primary gene pool of rice (Oryza meridionalis and Oryza rufipogon type taxa). Transcriptome profiling of all coding sequences in the genome revealed that genes were significantly differentially expressed at different stages of seed development in both wild and domesticated rice. Differentially expressed genes were associated with metabolism, transcriptional regulation, nucleic acid processing, and signal transduction with the highest number of being linked to protein synthesis and starch/sucrose metabolism. The level of gene expression associated with domestication traits, starch and sucrose metabolism, and seed storage proteins were highest at the early stage (5 days post anthesis (DPA)) to the middle stage (15 DPA) and declined late in seed development in both wild and domesticated rice. However, in contrast, black hull colour (Bh4) gene was significantly expressed throughout seed development. A substantial number of novel transcripts (38) corresponding to domestication genes, starch and sucrose metabolism, and seed storage proteins were identified. The patterns of gene expression revealed in this study define the timing of metabolic processes associated with seed development and may be used to explain differences in rice grain quality and nutritional value.

Unique Glutelin Expression Patterns and Seed Endosperm Structure Facilitate Glutelin Accumulation in Polyploid Rice Seed

BACKGROUND

Rice is not only an essential food but also a source of high quality protein. Polyploidy is an evolutionary trajectory in plants, and enhancing glutelin by polyploidization is an attractive strategy for improving the nutritional value of rice seeds and presents a great potential for enhancing the commercial value of rice. Elucidating the mechanisms underlying glutelin synthesis and accumulation in tetraploid rice is of great significance.

RESULTS

To enhance the nutritional value of rice, we developed tetraploid rice and evaluated the contents of various nutrient elements in mature seeds. The results revealed a significant increase in protein contents, including the total seed storage proteins, glutelins, and amino acids in tetraploid rice when compared with those in diploid rice. Tandem mass tag-based quantitative proteomic analyses of seeds revealed that glutelins regulated by several glutelin genes in 9311-4x were significantly up-regulated (≥1.5-fold), which was further verified by immunoblot analyses. In addition, temporal expression patterns of various glutelin subunits in different rice lines were investigated. The results revealed significant differences in the expression patterns between diploid and tetraploid rice seeds. Cytohistological analyses results revealed that the thickness of aleurone cell layers increased significantly by 32% in tetraploid rice, the structures of protein storage vacuoles (PSVs) in sub-aleurone cells were more diverse and abundant than those of diploid rice. Temporal expression and proteomic analyses results revealed that protein disulfide isomerase-like 1-1 expression levels were higher in tetraploid rice than in diploid rice, and that the gene responded to oxidative folding with increased levels of proglutelin and appropriate distribution of seed glutelins in tetraploid rice.

CONCLUSION

The results of the present study revealed that polyploidization increased glutelin content by influencing glutelin biosynthesis, transport, and deposition, while variations in glutelin accumulation between tetraploid and diploid rice were largely manifested in the initial time, duration, and relative levels of various glutelin gene expressions during seed filling stages. These findings provide novel insights into improving the protein quality and nutritional value of rice seeds by polyploid breeding.

Glutelin subtype-dependent protein localization in rice grain evidenced by immunodetection analyses

GluA and GluB-4/5 glutelin subfamilies are mainly localized to outer region of the endosperm, particularly in its ventral side, in rice grain, but GluC is localized to throughout the endosperm. The major seed storage protein in rice (Oryza sativa) is glutelin, which forms a vacuole-derived protein body type-II. Glutelins are encoded by multiple genes, and generally comprise four protein subfamilies, namely, GluA, GluB, GluC, and GluD: however, the localization pattern of glutelin in rice grains remains obscure. In this study, we investigated the localization pattern of five subtypes of the glutelin protein in rice grains using glutelin-subtype specific antibodies. Immunoblot analysis against sequentially polished rice flour fractions from three crop years and seven japonica rice varieties revealed that GluA was strongly localized in the outer region of the endosperm, including the subaleurone layer, whereas GluC was distributed throughout the endosperm. Among the glutelin subtypes, GluA was mostly found in the outer region of the rice grain, followed by GluB-4/5, GluB-1, GluD, and GluC. Immunofluorescence labeling microscopy analysis using immature rice seeds clearly revealed that the localization pattern of GluC and GluD was completely different from that of GluA and GluB. Expression levels of all glutelins, particularly GluA, GluB-1, and GluB-4/5, were stronger on the ventral than dorsal side in rice grains. These results provide strong and consistent evidence that glutelins localize to the rice grain in a subfamily-dependent manner.

Possible cleavage sites of glutelin partial degradation confirmed by immunological analysis in globulin-less mutants of rice (Oryza sativa L.)

Proteolytic cleavage or partial degradation of proteins is one of the important post-translational modifications for various biological processes, but it is difficult to analyze. Previously, we demonstrated that some subunits of the major rice (Oryza sativa L.) seed storage protein glutelin are partially degraded to produce newly identified polypeptides X1-X5 in mutants in which another major seed storage protein globulin is absent. In this study, the new polypeptides X3 and X4/X5 were immunologically confirmed to be derived from GluA3 and GluA1/GluA2 subunits, respectively. Additionally, the new polypeptides X1 and X2 were at least in part the α polypeptides of the GluB4 subunit partially degraded at the C-terminus. Simulated 2D-PAGE migration patterns of intact and partially degraded α polypeptides based on the calculation of their MWs and pIs enabled us to narrow or predict the possible locations of cleavage sites. The predicted cleavage sites were also verified by the comparison of 2D-PAGE patterns between seed-extracted and E. coli-expressed proteins of the intact and truncated α polypeptides. The results and methodologies demonstrated here would be useful for analyses of partial degradation of proteins and the structure-function relationships of rice seed protein bodies.

Functions of the CCCH type zinc finger protein OsGZF1 in regulation of the seed storage protein GluB-1 from rice

Glutelins are the most abundant storage proteins in rice grain and can make up to 80 % of total protein content. The promoter region of GluB-1, one of the glutelin genes in rice, has been intensively used as a model to understand regulation of seed-storage protein accumulation. In this study, we describe a zinc finger gene of the Cys3His1 (CCCH or C3H) class, named OsGZF1, which was identified in a yeast one-hybrid screening using the core promoter region of GluB-1 as bait and cDNA expression libraries prepared from developing rice panicles and grains as prey. The OsGZF1 protein binds specifically to the bait sequence in yeast and this interaction was confirmed in vitro. OsGZF1 is predominantly expressed in a confined domain surrounding the scutellum of the developing embryo and is localised in the nucleus. Transient expression experiments demonstrated that OsGZF1 can down-regulate a GluB-1-GUS (β-glucuronidase) reporter and OsGZF1 was also able to significantly reduce activation conferred by RISBZ1 which is a known strong GluB-1 activator. Furthermore, down-regulation of OsGZF1 by an RNAi approach increased grain nitrogen concentration. We propose that OsGZF1 has a function in regulating the GluB-1 promoter and controls accumulation of glutelins during grain development.

Identification and variation of glutelin alpha polypeptides in the genus Oryza assessed by two-dimensional electrophoresis and step-by-step immunodetection

To obtain fundamental information for nutritional improvement of rice (Oryza sativa) seed proteins, the alpha polypeptides of the major storage protein glutelin varied over the genus Oryza were qualitatively and quantitatively characterized with unique methods. The polypeptides were maximally separated by two-dimensional electrophoresis (2D-PAGE) composed of nonequilibrium pH gradient gel electrophoresis (NEPHGE) and higher temperature SDS-PAGE. Then the subunit for each polypeptide spot was identified with the sequential immunodetection called a step-by-step detection method, making use of highly subunit-specific antibodies. The comparative analysis showed considerable variation in the accumulation level of A-type and B-type glutelin subunits and found unknown glutelin subunits that were unable to be identified with the antibodies used. Wild species accumulating a high amount of lysine-rich B-type glutelin subunits and unknown unique subunits were identified as they might play a crucial role in nutritional quality improvement of the cultivated rice.

Endosperm-specific expression of serotonin N-hydroxycinnamoyltransferase in rice

Serotonin N-hydroxycinnamoyltransferase (SHT) is a key enzyme in the synthesis of feruloylserotonin (FS) and 4-coumaroylserotonin (CS). These serotonin derivatives show strong antioxidant activity, making them valuable for both nutritional and pharmacological use in humans. Ectopic expression of SHT under the control of the endosperm specific-glutelin and prolamin promoters from rice was produced via Agrobacterium-mediated transformation. SHT expression was confirmed by Southern blot analysis, followed by Northern blotting and SHT enzyme activity analyses using total RNA and protein, respectively, extracted from transgenic seeds. The glutelin A3 (GluA3) promoter produced low SHT mRNA expression in rice seeds, whereas the prolamin promoter expressed high levels of SHT mRNA. In spite of the ectopic expression of SHT in rice seeds, both transgenic genotypes accumulated levels of serotonin derivatives similar to those found in wild-type rice. Furthermore, our data suggest that serotonin, rather than phenylpropanid-CoAs, is the rate-limiting substrate in the biosynthesis of serotonin derivatives in SHT-overexpressing transgenic rice seeds.

Characterization of a new rice glutelin gene GluD-1 expressed in the starchy endosperm

A new glutelin gene, designated GluD-1, has been discovered by comparing the seed storage proteins from 48 japonica and indica rice cultivars on SDS-PAGE gels. Evidence that GluD-1 is a member of the glutelin family was provided by Western blots using anti-glutelin antiserum and by mapping the gene to the chromosomal glutelin gene cluster. The limited GluD-1 size polymorphism among the rice varieties is due to amino acid substitutions rather than to post-transcriptional modification. GluD-1 is maximally expressed in the starchy endosperm starting at 5 d after flowering (DAF) and increasing through 30 DAF, a major difference from the other glutelins which are primarily expressed in the subaleurone from 10-16 DAF. Only about 0.2 kb of the GluD-1 promoter was sufficient to confer inner starchy endosperm-specific expression. The 0.2 kb truncated GluD-1 promoter contains a bifactorial endosperm box consisting of a truncated GCN4 motif (TGA(G/C)TCA) and AAAG Prolamin box (P box), and ACGT and AACA motifs as cis-regulatory elements. Gel retardation assays and trans-activation experiments indicated that the truncated GCN4 and P box are specifically recognized by RISBZ1 b-ZIP and RPBF Dof activators in vitro, respectively, and are synergistically transactivated, indicating that combinatorial interactions of these motifs are involved in essential endosperm-specific regulation. Furthermore, deviation from the cognate GCN4 motif alters tissue-specific expression in the inner starchy endosperm to include other endosperm tissues.

Expression of the fusion glycoprotein of newcasstle disease virus in transgenic rice and its immunogenicity in mice

Transgenic plant has become an attractive bioreactor to produce high-value medical peptides and proteins in biomedical research. In present study, two expression cassettes, pUNDVF and pGNDVF containing the fusion protein gene of Newcastle disease virus (NDV F) under the control of maize ubiquitin (Ubi) promoter or rice glutelin (Gt1) promoter, respectively, were constructed, and introduced into rice (Oryzy sativa L.) by Agrobacterium-mediated transformation. A total of 12 independent transgenic rice lines were regenerated, and the result from PCR analysis indicated that the T-DNA region containing the NDV F chimeric gene had been integrated into the genome of transgenic rice plants. ELISA and Western-blot analyses revealed that the NDV F protein could be expressed and accumulated in both leaf and seed tissue of several transgenic rice plants. Moreover, the immunogenicity of expressed proteins was tested in a mouse model and the results showed that specific antibodies were elicited in mice immunized intraperitoneally with crude protein extracts from transgenic rice plants. It implied the potential of using transgenic rice-based expression systems as supplementary bioreactor for NDV engineering subunit vaccine.

Synergism between RPBF Dof and RISBZ1 bZIP activators in the regulation of rice seed expression genes

The Dof (DNA binding with one finger) transcriptional activator rice (Oryza sativa) prolamin box binding factor (RPBF), which is involved in gene regulation of rice seed storage proteins, has been isolated from rice cDNA expressed sequence tag clones containing the conserved Dof. RPBF is found as a single gene per haploid genome. Comparison of RPBF genomic and cDNA sequences revealed that the genomic copy is interrupted by one long intron of 1,892 bp in the 5' noncoding region. We demonstrated by transient expression in rice callus protoplasts that the isolated RPBF trans-activated several storage protein genes via an AAAG target sequence located within their promoters, and with methylation interference experiments the additional AAAG-like sequences in promoters of genes expressed in maturing seeds were recognized by the RPBF protein. Binding was sequence specific, since mutation of the AAAG motif or its derivatives decreased both binding and trans-activation by RPBF. Synergism between RPBF and RISBZ1 recognizing the GCN4 motif [TGA(G/C)TCA] was observed in the expression of many storage protein genes. Overexpression of both transcription factors gave rise to much higher levels of expression than the sum of individual activities elicited by either RPBF or RISBZ1 alone. Furthermore, mutation of recognition sites suppressed reciprocal trans-activation ability, indicating that there are mutual interactions between RISBZ1 and RPBF. The RPBF gene is predominantly expressed in maturing endosperm and coordinately expressed with seed storage protein genes, and is involved in the quantitative regulation of genes expressed in the endosperm in cooperation with RISBZ1.

The GCN4 motif in a rice glutelin gene is essential for endosperm-specific gene expression and is activated by Opaque-2 in transgenic rice plants

The GCN4 motif is conserved in a number of seed storage protein genes, and promoter fragments containing this motif have been shown to be involved in controlling seed-specific expression of the genes studied. All genes encoding the rice seed storage protein glutelin contain the GCN4 motif at similar sites in their 5' flanking regions. Using a stable homologous transgenic system, we have analysed the promoter of the rice glutelin gene GluB-1 and demonstrated that the GCN4 motif functions as an essential cis-element for endosperm-specific gene expression. Moreover, a 21 bp GluB-1 promoter fragment spanning the GCN4 motif, as a multimer, directed GUS gene expression in endosperm of transgenic rice plants, when fused directly to the core promoter (-46) of CaMV 35S. In transiently transfected rice protoplasts, over a hundred-fold transactivation was observed from the 21 bp sequence by the bZIP type transcriptional activator Opaque-2 (O2) co-expressed under a CaMV 35S promoter. The transactivation was also evident in transgenic plants containing both O2 and the 21 bp sequence/GUS fusion. The O2-mediated activation requires binding of O2 to an intact GCN4 motif. Our results suggest that a bZIP protein functionally similar to O2 may exist in rice and participate in controlling the endosperm-specific expression of GluB-1 through the GCN4 motif.

Cloning and expression of five myb-related genes from rice seed

Three elements in the promoter of rice glutelin genes are important for their endosperm specific expression. One of these, an AACA motif, has been shown to be a negative regulator in non-seed tissues and has a similarity to the barley gibberellin responsive element recognized by MYB-like DNA binding proteins. A cDNA library constructed from immature rice seed was screened using two types of myb gene probes to isolate cDNA clones representing genes encoding MYB-like DNA binding proteins that may recognize the AACA motif in rice glutelin gene promoter. We obtained four cDNA clones encoding MYB-related proteins, Oryza sativa MYB (OSMYB) 1-4, using the maize C1 probe. Another myb-like clone, Osmyb5, was obtained by screening a rice seed cDNA library with probes designed to recognize the AACA-like binding domain in GAMYB and PHMYB3. RT-PCR was used to analyze Osmyb expression during rice seed development and their presence in other rice tissues, as it was not possible to detect these mRNAs by conventional Northern analysis. RT-PCR analysis showed that Osmyb2, Osmyb3 and Osmyb5 genes were expressed in all tissues examined. In seed, the mRNA levels of Osmyb1 and Osmyb4 genes reached a maximum at 14 days after flowering (DAF), suggesting that these genes may play a role in seed maturation. As Osmyb5 exhibits a high similarity to the regions in both GAMYB and PHMYB3, which can bind to the AACA motif, there is a possibility that the OSMYB5 protein may bind to the AACA motif of glutelin genes.

A 45-bp proximal region containing AACA and GCN4 motif is sufficient to confer endosperm-specific expression of the rice storage protein glutelin gene, GluA-3

A 45-bp proximal region of the rice glutelin promoter (-104/-60) containing two putative cis-elements, the AACA motif and GCN4 motifs, was fused to a truncated CaMV 35S promoter (-90/+9; -90 delta 35S)/GUS. The 45-bp fragment specifically enhanced the promoter activity in endosperm tissue of transformed tobacco. A substitution mutation of the GCN4 motif reduced the promoter activity, whereas mutation of the AACA motif increased the activity in the embryo as well as in the endosperm. These results suggest that the GCN4 motif generally enhances the promoter activity but that the combination of the two motifs confers the endosperm specificity. Furthermore, the function of the two motifs was dependent on the orientation and/or distance from a G-box element in -90 delta 35S, suggesting that synergistic interaction between the factors that recognize those motifs and the G-box element is important for transcriptional regulation.

Characterization of common cis-regulatory elements responsible for the endosperm-specific expression of members of the rice glutelin multigene family

Glutelin is the most abundant storage protein in rice, which is expressed specifically in the endosperm of maturing seed. Glutelin is encoded by about 10 genes per haploid genome, which are clearly divided into two subfamilies (GluA and GluB). Most of them are coordinately expressed during seed maturation in spite of the remarkable divergence in the 5'-flanking regions between members of two subfamilies. In order to identify the common regulatory mechanisms responsible for the endosperm-specific expression, various cis-regulatory elements in the 5'-flanking region of the glutelin GluB-1 gene were characterized by studying the expression of chimeric genes that consisted of the sequentially deleted or mutagenized promoter and a beta-glucuronidase (GUS) reporter gene in transgenic tobacco seeds. The essential cis-regulatory elements governing the spatially and temporally specific expression of the glutelin gene expression were located within the first 245 bp of the promoter region of the GluB-1 gene from the site of initiation of transcription. The AACA motif between positions -73 and -61 common to all the six genes for glutelin sequenced to date and is repeated between positions -212 and -200 is implicated in the seed-specific expression. The GCN4 motif between positions -165 and -158 and between positions -96 and -92 that is conserved at homologous sites in all the members of glutelin gene family is also involved in the seed-specific regulation. However, both are required for the high level of seed-specific expression, because deletion of the region containing one set of both elements or substitution mutation of the AACA or GCN4 motif substantially reduced the activity. As a whole, our results suggest the combinatorial interaction of the elements in regulation of the glutelin gene expression.

Legumin-like and vicilin-like seed storage proteins: evidence for a common single-domain ancestral gene

Legumin-like 11S and vicilin-like 7S globulins are the main storage proteins of most angiosperms and gymnosperms. The subunits of the hexameric legumin are synthesized as a precursor comprising a N-terminal acidic alpha- and a C-terminal basic beta-chain. The trimeric vicilin molecule consists of subunits composed of two symmetrical N- and C-terminal structural domains. In a multiple alignment we have compared the N-terminal and C-terminal domains of 11 legumins and seven vicilins of several dicot, monocot, and gymnosperm species. The comparisons using all six possible pairwise combinations reveal that the N-terminal and C-terminal domains of both protein families are similar to each other. These results together with data on the distribution of variable and conserved regions, on the positions of susceptible sites for proteolytic attack, as well as on the published 7S protein tertiary structure suggest that both protein families share a common single-domain ancestor molecule and lead to the hypothesis that a triplication event has occurred during the evolution of a putative legumin/vicilin ancestor gene. Moreover, the comparison of the intron/exon pattern reveals that at least three out of five intron positions are precisely conserved between the genes of both protein families, further supporting the idea of a common evolutionary origin of recent legumin and vicilin encoding genes.

Evolution of seed storage protein genes: legumin genes of Ginkgo biloba

Legumin-like seed storage proteins have been intensively studied in crop plants. However, little is known about the molecular evolution of these proteins and their genes and it was assumed that they originated from an ancestral gene that already existed at the beginning of angiosperm evolution. We have evidence for the ubiquitous occurrence of homologous proteins in gymnosperms as well. We have characterized the major seed storage globulin from Ginkgo biloba by amino acid sequencing, which reveals clear homology to legumin-like proteins from angiosperms. The Ginkgo legumin is encoded by a gene family; we describe two of its members. The promoter regions contain sequence motifs which are known to function as regulatory elements involved in seed-specific expression of angiosperm legumins, although the tissues concerned are different in gymnosperms and angiosperms. The Ginkgo legumin gene structure is divergent from that of angiosperms and suggests that the evolution of legumin genes implicated loss of introns. From our data and from functional approaches recently described it becomes obvious that the posttranslational processing site of legumin precursors is less conserved than hitherto assumed. Finally, we present a phylogenetic analysis of legumin encoding sequences and discuss their utility as molecular markers for the reconstruction of seed plant evolution.

Tissue-specific expression and temporal regulation of the rice glutelin Gt3 gene are conferred by at least two spatially separated cis-regulatory elements

The rice glutelin Gt3 promoter was fused to a beta-glucuronidase (GUS) reporter gene and its expression evaluated in transgenic tobacco plants. Histochemical analysis revealed that the expression of the introduced Gt3 promoter/GUS (beta-glucuronidase) chimeric gene was confined to endosperm tissue of developing seeds. 5'-promoter deletion analysis revealed that two domains of the Gt3 promoter, -346 to -263 bp (domain I) and -945 to -726 bp (domain II) from the transcriptional start site, were essential for optimum expression of the GUS reporter gene. Removal of 5' sequences upstream of -726 resulted in a reduction in overall promoter activity and a shift in temporal expression from a maximum of 16-20 days after flowering to 24 days. Removal of DNA sequences from the 5' end to -346 yielded a promoter fragment that was still able to confer endosperm-specific expression, although a further deletion to -263 abolished promoter activity. These data suggest that at least two cis-regulatory elements are required for endosperm specificity and temporal regulation of glutelin Gt3 gene expression.

Sequence of three members and expression of a new major subfamily of glutelin genes from rice

Three members have been isolated of an additional glutelin gene subfamily, named subfamily B, consisting of about five members per haploid rice genome. Restriction fragment length polymorphism analysis showed major differences between Japonica and Indica lines, indicating the divergence of the subfamily since the split between the two varieties. While corresponding exons of the subfamily B showed 80 to 88% nucleotide sequence homology, those exons were only 60-65% homologous to those of the glutelin A subfamily, distinguishing them from the subfamily A. Intron position and derived polypeptide structure, in addition to the nucleotide sequence, confirm the subfamily B members as glutelins. Analysis of RNA from seeds of different stages of development showed that the subfamily B members were expressed at the same time as those of subfamily A, demonstrating coordinated regulation of the two subfamilies.