Characterization of a Radish Nuclear Gene Expressed during Late Seed Maturation

Abstract

To study long-lived mRNAs stored in radish (Raphanus sativus) seed, we have selected clones from a dry seed cDNA library by differential screening. One of these clones, p8B6, whose mRNAs are abundant in the dry seed, was characterized. This clone hybridizes to an RNA class of approximately 600 nucleotides whose accumulation begins during the desiccation phase, reaches its maximum level in the dry seed, and is no longer detectable in 12 hour old seedlings. mRNAs hybrid-selected by p8B6 encode four polypeptides, but only two are compatible with the size class of RNAs detected by Northem analysis. Three of them have previously been identified as major 'early germination' polypeptides, and their synthesis has been shown to be induced prematurely in immature embryos by a desiccation treatment. The protein deduced from the p8B6 nucleotide sequence is 9 kilodaltons in size, highly hydrophilic, rich in Gly and Glu, and contains no Cys, Trp, and lie. The amino acid sequence shares good homology with that of two recently described seed proteins: a cotton late embryogenesis abundant protein and the wheat early methionine-labeled protein. Southem blot analysis suggests that the p8B6 sequence belongs to a very small gene family. The exact function of the product encoded by p8B6 remains to be determined.Dry seed embryos contain translatable stored mRNAs, which encode the first proteins synthesized during imbibition (1,3,22,25). However, the nature, origin, and function of the proteins encoded by these long-lived mRNAs remain unclear. Do they correspond to embryogenesis-specific polypeptides or do they play an essential role during early germination? To answer this question, several groups (1,24,25) have analyzed proteins and mRNA at different stages of development. Proteins were analyzed by staining, while the mRNA population was studied by radioactive labeling of proteins in vivo or by an in vitro translation system. Up to now, several major gene families have been distinguished by their differential expression (1,4,23,24

Distribution of Cytosolic mRNAs Between Polysomal and Ribonucleoprotein Complex Fractions in Alfalfa Embryos

“…The paired somatic. heart somatic *cot (b) monosomes and small polysomes (fractions [5][6][7][8][9], and (c) large polysomes (fractions [10][11][12][13][14][15][16][17][18][19][20][21][22] were used for northern blot analysis against probes for the major 1 Figure 5 show the synthesis of proteins from polysomal mRNAs and those in the mRNP fraction extracted from the transition stages of developing somatic and zygotic embryos, i.e. when the patterns of storage protein synthesis change (Fig.…”

“…Stagespecific activation of different mRNA species is also common during early embryogenic development in the surf clam (22). The presence and importance of mRNPs in plants has not been subjected to intensive study, although there is ample evidence for the presence of 'stored' mRNAs in RNPs in the mature dry seed (10,18,20,24). Their presence during embryogenesis is uncertain, although it has been reported that the mRNA for the ,B subunit of 13-conglycinin increases several days before the accumulation of the protein (14).…”

Characterization of a Gene That Is Expressed Early in Somatic Embryogenesis of Daucus carota

“…Genes homologous to the emb-l gene may be expressed in all monocot and dicot embryos (Cuming, 1984;Litts et al, 1987;Baker et al, 1988;Raynal et al, 1989;Ulrich et al, 1990;Williams and Tsang, 1991;Espelund et al, 1992). Genes from cotton (Leu D19 gene) and from wheat (Em gene) that code for proteins similar to that encoded by EMB-1 are expressed primarily at the time of embryo desiccation or in response to ABA (Dure et al, 1989;Marcotte et al, 1989;Hughs and Galau, 1991).…”

Stress hydrique: étude des mécanismes moléculaires et des modifications de l'expression du génome

“…Cette dernière a longtemps été considérée comme un phénomène passif. Des travaux récents sur l'expression des gènes au cours des différentes phases du développement des graines ont montré que de nombreux gènes sont spécifiquement induits pendant la phase de maturation (Mundy et Chua, 1988 ;Raynal et al, 1989), qui pourraient contribuer à la tolérance de la dessication (Pradet et Raymond, 1990).…”

“…Chez le radis certains gènes présentent un taux maximal de transcrits dans la graine sèche (Raynal et al, 1989) ; certains des polypeptides codés par ces gènes, sont exprimés en début de germination, pendant les 15 premières minutes, et leurs synthèses prématurées, pendant l'embryogenèse, peuvent être induites par un traitement déshydratant (Aspart et al, 1984 ;Raynal et al, 1989). b) A l'hydratation La prolifération membranaire et la synthèse simultanée de protéines sont rapidement induites au cours de l'imbibition des graines.…”