Earlier studies found that cotton (Gossypium hirsutum L.) cotyledons contain several mRNAs which are more abundant during late embryogenesis than in mid-embryogenesis or early germination. They are here termed 'Late embryogenesis-abundant' mRNAs, encoded by Lea loci. Complementary DNA clones for 18 such mRNA sequences, defined at a hybridization criterion of Tm-15°C, were identified in a mature embryo cDNA library by differential cDNA hybridization. At a lower hybridization criterion, some sequence homology was found within several of these cloned Lea mRNA sequences. Each Lea mRNA sequence comprises 0.04-1.3% of mature embryo poly(A)(+) mRNA, a level ten-fold to several hundred-fold higher than in young embryo or 24 h seedling poly(A)(+) mRNA. Of 18 Lea mRNA sequences examined in cultured young embryos, the level of at least 13 are specifically increased by exogenous abscisic acid (ABA), several to a level near that in normal mature embryos. However, the abundance of several of the sequences does not appear to be significantly modulated by ABA. The LEA polypeptides encoded by 10 Lea mRNA sequences were identified by hybrid-arrested translation. They include most of the late embryogenesis-abundant, ABA-inducible, polypeptides previously identified. Preliminary results suggest that many of the individual Lea mRNA sequences are transcribed from 1-3 genes in each of cotton's two subgenomes.

In Ricinus communis L. (castor bean) endosperms, two classes of Late Embryogenesis Abundant (Lea) transcripts were first detected during mid-development (at 30-35 days after pollination, DAP) and peaked at 50 DAP, just prior to the onset of desiccation. Most of the Class I mRNAs declined substantially during desiccation itself; Class II mRNAs remained abundant in the mature dry (60 DAP) seed. Following imbibition, all Lea mRNAs abundant in the mature dry seed declined rapidly (within 5-24 h). Premature drying of developing 35-DAP seeds resulted in the loss of storage-protein mRNAs (Leg B Mat I); following rehydration, mRNAs encoding post-germinative proteins (Germ D91, D30 and D38) increased in the endosperm. The Lea mRNAs present in the developing fresh seed at 35 DAP were preserved, but did not increase in response to premature desiccation; upon rehydration these Lea mRNAs declined within 5 h. During seed development, substantial changes occurred in the synthesis of a subset of LEA proteins referred to as "dehydrins'; in particular, new dehydrin polypeptides were induced between 40 and 60 DAP. Such proteins were not as evident in prematurely dried endosperms. In contrast to the rapid loss of Lea mRNAs during germination, many of the dehydrin proteins abundant in the dried seed persisted following imbibition or rehydration.

To study the control of enhanced synthesis of enzymes associated with C4 photosynthesis relative to non-C4 plants, we investigated the expression of NADP-malic enzyme (NADP-ME) in different photosynthetic types of Flaveria. Complementary DNA clones encoding NADP-ME were constructed using poly(A)+ RNA from leaves of Flaveria trinervia (C4) and F. linearis (C3-C4) and identified by homology to a cDNA clone (500 bp) encoding NADP-ME from maize (Zea mays L. [39]). The sequence of one clone from each species was determined. The Flaveria clones were 90% homologous over a 564 nucleotide region encoding the carboxy terminal end of the derived polypeptide; sequence similarity to the maize transcript in this region was 71%. Both Flaveria clones detected a 2/3 kb transcript by hybridization to poly(A)+ RNA from expanding leaves of F. trinervia, F. linearis and F. pringlei (C3). The level of transcripts paralleled previously observed NADP-ME activity and abundance differences determined in these species, suggesting that control of the expression of NADP-ME in different photosynthetic types is predominantly at the transcriptional/post-transcriptional level. Southern analysis of genomic DNAs from F. trinervia, F. linearis and F. pringlei indicated a low copy number for this gene in all three species.

We have determined the copy number of 21 genes in an allotetraploid and several diploid species of cotton by gel and dot blot hybridization with cloned cDNAs. The legumin A, legumin B, and all 18 unique Lea (late embryogenesis-abundant) cDNA sequences isolated from the AD allotetraploid Gossypium hirsutum are present in one copy in A, D, E, and F diploid species and in two copies in G. hirsutum. Gel blot analysis of DNAs digested with EcoRI or BamHI usually detects different sized fragments in A and D diploids. Conservation of these restriction fragment length polymorphisms in G. hirsutum allows most of these fragments to be assigned to their respective subgenomes. Furthermore, both subgenomes in G. hirsutum can be distinguished from those in the interfertile allotetraploid G. barbadense. These results show that physical mapping of both sets of chromosomes in an allotetraploid should be possible by segregation analysis.