Teosinte (Zea mays ssp parviglumis) growth and transcriptomic response to weed stress identifies similarities and differences between varieties and with modern maize varieties.

Transcriptomic responses of plants to weed presence gives insight on the physiological and molecular mechanisms involved in the stress response. This study evaluated transcriptomic and morphological responses of two teosinte (Zea mays ssp parviglumis) (an ancestor of domesticated maize) lines (Ames 21812 and Ames 21789) to weed presence and absence during two growing seasons. Responses were compared after 6 weeks of growth in Aurora, South Dakota, USA. Plant heights between treatments were similar in Ames 21812, whereas branch number decreased when weeds were present. Ames 21789 was 45% shorter in weedy vs weed-free plots, but branch numbers were similar between treatments. Season-long biomass was reduced in response to weed stress in both lines. Common down-regulated subnetworks in weed-stressed plants were related to light, photosynthesis, and carbon cycles. Several unique response networks (e.g. aging, response to chitin) and gene sets were present in each line. Comparing transcriptomic responses of maize (determined in an adjacent study) and teosinte lines indicated three common gene ontologies up-regulated when weed-stressed: jasmonic acid response/signaling, UDP-glucosyl and glucuronyltransferases, and quercetin glucosyltransferase (3-O and 7-O). Overall, morphologic and transcriptomic differences suggest a greater varietal (rather than a conserved) response to weed stress, and implies multiple responses are possible. These findings offer insights into opportunities to define and manipulate gene expression of several different pathways of modern maize varieties to improve performance under weedy conditions.

Cloning and characterization of cold-regulated glycine-rich RNA-binding protein genes from leafy spurge (Euphorbia esula L.) and comparison to heterologous genomic clones.

Leafy spurge (Euphorbia esula) is a perennial weed which is capable of acclimating to sub-freezing temperatures. We have used the differential display technique to identify and clone a cDNA for a cold-regulated gene (cor20) which hybridizes to mRNAs that accumulate specifically during the cold acclamation process. The cor20 cDNA was used to isolate two different genomic clones. Both clones were similar but not identical to each other and the cDNA. Sequence analysis of the genomic clones indicated that they share considerable homology to a group of glycine-rich RNA-binding protein genes. Comparison of the promoter region from the three clones (Ccr1 from Arabidopsis. BnGRP10 from Brassica napus, and GRRBP2 from Euphorbia esula) have identified at least two conserved motifs. CAGC is most likely involved in cold regulation and AACCCYAGTTA, is conserved but has no known function. RNAs which hybridize to cor20 reach maximal expression in less than 2 days after exposure of the plant to temperatures of 5 degrees C, and remains at high levels in the plant for at least 30 days so long as the plant is left in the cold. These RNAs drop to control levels within 24 h when the plant is returned to normal growing temperatures. Transcripts which hybridize to cor20 do not accumulate under conditions of drought or heat stress. These transcripts are induced in response to low temperatures in roots, stems and leaves, but are expressed constitutively in tissue culture at control temperatures.

Regulation of Arabidopsis thaliana L. (Heyn) cor78 in response to low temperature.

Changes in gene expression occur during cold acclimation in a variety of plants including Arabidopsis thaliana L. (Heyn). Here we examine the cold-regulated expression of A. thaliana cor78. The results of gene-fusion experiments confirm the finding of Yamaguchi-Shinozaki and Shinozaki ([1993] Mol Gen Genet 236: 331-340) that the 5' region of cor78 has cis-acting regulatory elements that can impart cold-regulated gene expression. Further, histochemical staining experiments indicated that this cold-regulatory element(s) was active at low temperature throughout much of the plant including leaves, stems, roots, flower petals, filaments, and sepals. Time-course experiments indicated that the activity of the cor78 promoter in cold-acclimated plants was down-regulated quickly in response to noninducing temperatures and that the half-life of the cor78 transcripts was only about 40 min at normal growth temperature. Fusion of the entire transcribed region of cor78 to the cauliflower mosaic virus 35S promoter resulted in a chimeric gene that was constitutively expressed and displayed little if any posttranscriptional regulation in response to low temperature.

Molecular Cloning and Expression of cor (Cold-Regulated) Genes in Arabidopsis thaliana.

We have previously shown that changes in gene expression occur in Arabidopsis thaliana. L. (Heyn) during cold acclimation (SJ Gilmour, RK Hajela, MF Thomashow [1988] Plant Physiol 87: 745-750). Here we report the isolation of cDNA clones of four cold-regulated (cor) genes from Arabidopsis and examine their expression in response to low temperature, abscisic acid (ABA), water stress, and heat shock. The results of Northern analysis indicated that the transcript levels for the four cor genes, represented by clones pHH7.2, pHH28, pHH29, and pHH67, increased markedly between 1 and 4 hours of cold treatment, reached a maximum at about 8 to 12 hours, and remained at elevated levels for as long as the plants were kept in the cold (up to 2 weeks). Returning cold acclimated plants to control temperature resulted in the levels of the cor transcripts falling rapidly to those found in nonacclimated plants; this occurred within 4 hours for the transcripts represented by pHH7.2 and pHH28, and 8 hours for those represented by pHH29 and pHH67. Nuclear run-on transcription assays indicated that the temperature-regulated expression of the cor genes represented by pHH7.2, pHH28, and pHH29 was controlled primarily at the posttranscriptional level while the cor gene represented by pHH67 was regulated largely at the transcriptional level. Northern analysis also indicated that the levels of cor gene transcripts increased in response to both ABA application and water stress, but not to heat shock. The possible significance of cor genes being regulated by both low temperature and water stress is discussed.