A minimal peach type II chlorophyll a/b-binding protein promoter retains tissue-specificity and light regulation in tomato

<p>Abstract</p> <p>Background</p> <p>Promoters with tissue-specificity are desirable to drive expression of transgenes in crops to avoid accumulation of foreign proteins in edible tissues/organs. Several photosynthetic promoters have been shown to be strong regulators of expression of transgenes in light-responsive tissues and would be good candidates for leaf and immature fruit tissue-specificity, if expression in the mature fruit were minimized.</p> <p>Results</p> <p>A minimal peach chlorophyll <it>a/b</it>-binding protein gene (<it>Lhcb2*Pp1</it>) promoter (Cab19) was isolated and fused to an <it>uid</it>A (β-glucuronidase [GUS]) gene containing the PIV2 intron. A control vector carrying an enhanced <it>mas</it>35S CaMV promoter fused to <it>uid</it>A was also constructed. Two different orientations of the Cab19::GUS fusion relative to the left T-DNA border of the binary vector were transformed into tomato. Ten independent regenerants of each construct and an untransformed control line were assessed both qualitatively and quantitatively for GUS expression in leaves, fruit and flowers, and quantitatively in roots.</p> <p>Conclusion</p> <p>The minimal CAB19 promoter conferred GUS activity primarily in leaves and green fruit, as well as in response to light. GUS activity in the leaves of both Cab19 constructs averaged about 2/3 that observed with <it>mas</it>35S::GUS controls. Surprisingly, GUS activity in transgenic green fruit was considerably higher than leaves for all promoter constructs; however, in red, ripe fruit activities were much lower for the Cab19 promoter constructs than the <it>mas</it>35S::GUS. Although GUS activity was readily detectable in flowers and roots of <it>mas</it>35S::GUStransgenic plants, little activity was observed in plants carrying the Cab19 promoter constructs. In addition, the light-inducibility of the Cab19::GUS constructs indicated that all the requisite <it>cis</it>-elements for light responsiveness were contained on the Cab19 fragment. The minimal Cab19 promoter retains both tissue-specificity and light regulation and can be used to drive expression of foreign genes with minimal activity in mature, edible fruit.</p

Complementary regulation of four Eucalyptus CBF genes under various cold conditions

CBF transcription factors play central roles in the control of freezing tolerance in plants. The isolation of two additional CBF genes, EguCBF1c and EguCBF1d, from E. gunnii, one of the cold-hardiest Eucalyptus species, is described. While the EguCBF1D protein sequence is very similar to the previously characterized EguCBF1A and EguCBF1B sequences, EguCBF1C is more distinctive, in particular in the AP2-DBD (AP2-DNA binding domain). The expression analysis of the four genes by RT-qPCR reveals that none of them is specific to one stress but they are all preferentially induced by cold, except for the EguCBF1c gene which is more responsive to salt. The calculation of the transcript copy number enables the quantification of constitutive CBF gene expression. This basal level, significant for the four genes, greatly influences the final EguCBF1 transcript level in the cold. A cold shock at 4 °C, as well as a progressive freezing which mimics a natural frost episode, trigger a fast and strong response of the EguCBF1 genes, while growth at acclimating temperatures results in a lower but more durable induction. The differential expression of the four EguCBF1 genes under these cold regimes suggests that there is a complementary regulation. The high accumulation of the CBF transcript, observed in response to the different types of cold conditions, might be a key for the winter survival of this evergreen broad-leaved tree

Modulation of Dormancy and Growth Responses in Reproductive Buds of Temperate Trees

During autumn perennial trees cease growth and form structures called buds in order to protect meristems from the unfavorable environmental conditions, including low temperature and desiccation. In addition to increased tolerance to these abiotic stresses, reproductive buds modulate developmental programs leading to dormancy induction to avoid premature growth resumption, and flowering pathways. Stress tolerance, dormancy, and flowering processes are thus physically and temporarily restricted to a bud, and consequently forced to interact at the regulatory level. We review recent genomic, genetic, and molecular contributions to the knowledge of these three processes in trees, highlighting the role of epigenetic modifications, phytohormones, and common regulatory factors. Finally, we emphasize the utility of transcriptomic approaches for the identification of key structural and regulatory genes involved in bud processes, illustrated with our own experience using peach as a model

Application of BABA and s-ABA for drought resistance in apple

Limited fresh water is a global problem that adversely affects crops, including young apple (Malus × domestica) trees. Innovative technologies will be needed to ensure tree survival and productivity. Recently, selected chemicals have been used to prepare plants for avoidance and recovery from water stress by a process termed priming. Two priming compounds, abscisic acid (ABA) and DL- β-aminobutyric acid (BABA) have been shown to confer plant protection against a range of biotic and abiotic stresses. Our objective was to determine the resistance to and recovery from dehydration of apple seedlings treated with s-ABA and BABA. Three greenhouse experiments were conducted in which combinations of s-ABA and BABA were applied as a root drench to one-year-old ‘Royal Gala’ apple trees and responses to dehydration were evaluated. Changes in leaf water potential (ψw), stomatal conductance (gs), transpiration (E), leaf ABA and growth were measured during dehydration and rehydration. In two experiments, pretreatment with BABA reduced early morning E but BABA was not as effective as s-ABA in delaying dehydration-induced wilt of shoot tips. In another experiment during the second week without water both BABA- and s-ABA-treated trees had 42 to 62% higher leaf ψw, respectively, and 45% lower leaf ABA than unwatered controls. Higher leaf ψw was not consistently associated with reduced gs and E suggesting that mechanisms other than increased stomatal resistance may provide drought resistance. Compared with control trees, there was nearly 80% more shoot growth following rewatering after dehydration in trees that were primed with BABA and s-ABA (1.0 mM each). Leaf senescence was more evident in s-ABA- than BABA-treated trees and, although growth resumed after dehydration, the amount of growth varied with concentration of the priming treatments. Both individual compounds provided dehydration protection to young apple trees but in combination they were not clearly superior to either compound alone

Involvement of cytosolic ascorbate peroxidase and Cu/Zn-superoxide dismutase for improved tolerance against drought stress

In order to understand the role of cytosolic antioxidant enzymes in drought stress protection, transgenic tobacco (Nicotiana tabacum cv. Xanthi) plants overexpressing cytosolic Cu/Zn-superoxide dismutase (cytsod) (EC 1.15.1.1) or ascorbate peroxidase (cytapx) (EC 1.11.1.1) alone, or in combination, were produced and tested for tolerance against mild water stress. The results showed that the simultaneous overexpression of Cu/Znsod and apx or at least apx in the cytosol of transgenic tobacco plants alleviates, to some extent, the damage produced by wáter stress conditions. This was correlated with higher water use efficiency and better photosynthetic rates. In general, oxidative stress parameters, such as lipid peroxidation, electrolyte leakage, and H2O2 levels, were higher in non-transformed plants than in transgenic lines, suggesting that, at the least, overexpression of cytapx protects tobacco membranes from water stress. In these conditions, the activity of other antioxidant enzymes was induced in transgenic lines at the subcellular level. Moreover, an increase in the activity of some antioxidant enzymes was also observed in the chloroplast of transgenic plants overexpressing cytsod and/or cytapx. These results suggest the positive influence of cytosolic antioxidant metabolism on the chloroplast and underline the complexity of the regulation network of plant antioxidant defences during drought stress.This work was supported by BIOCARM BIO-AGR07/ 04-0011, CICYT AGL2006-01743/AGR, and CICYT BFU2009-07443. MF was supported by a ‘Ramo´n & Cajal’ contract from the Spanish Ministry of Education. GBE thanks the CSIC for his JAE research fellowship. MJCM thanks the Spanish Ministry of Science and Education for her FPI research fellowship.Peer reviewe