Abstract: Although suboptimal temperatures during maize (Zea mays L) seedling growth are known to result in decreased photosynthetic efficiency due to a combination of temperature and light stress, details remain scant on the impact of low night temperatures on photosynthetic activity. To better understand the role of night temperature on the acclimation of the photosynthetic apparatus to suboptimal temperature, a QTL experiment was conducted with the IBM302 population. Seedlings were grown under optimal temperature (24/22°C, day/night) or under subopti¬mal temperatures (17°C day and 6 or 13°C night). The two parental lines, B73 and Mo17, responded somewhat differently to suboptimal temperatures, as revealed by measurements of the operating quantum efficiency of PS II (Fq’/Fm’), the maximum quantum efficiency of PS II primary photochemistry (Fv/Fm) and leaf greenness (SPAD). While Mo17 showed very little change in response to the temperature at night, B73 exhibited a lower photosyn¬thetic performance at 13°C than at 6°C at night. At 17/6°C the photosynthetic efficiency of both genotypes was similar. These observations were supported by QTL analyses. A major QTL for photosynthesis-related traits was detected on chromosome 5 with the favorable allele contributed by Mo17. This QTL showed a lower additive effect at a temperature of 6°C than at 13°C during the night and appeared to be the major factor explaining the differential response of the parental lines to changes in the temperature at night. As potential candidate genes for this locus, ivr2 (coding for an acid vacuolar invertase) and a2 (coding for an anthocyanidin synthase) were identi¬fied. QTL analyses for invertase activity and anthocyanin content revealed a QTL for invertase activity near the ivr1 gene and a QTL for anthocyanin content close to the r1 locus, both, however, were not related to the major QTL for photosynthesis-related traits. Comparative QTL analyses of photosynthetic traits of this population and other pulished studies revealed conserved QTL regions on chromosomes 6 and 8.
Abstract: Maize (Zea mays L.) is an important crop that is poorly adapted to cold stress; very little is known about the components of the response to stress. By means of the cDNA subtraction technique, several novel genes, responsive to cold stress, have been identified, including ZmCOI6.1, the function of which is unknown. The predicted ZmCOI6.1 amino acid sequence and its homologue are very similar to proteins in rice and Arabidopsis, suggesting that it belongs to a conserved group of plant proteins. Analysis of the ZmCOI6.1 promoter sequence revealed several conserved stress-responsive cis-acting elements. Further characterization of expression showed that ZmCOI6.1 was induced not only by cold, but also by drought and salinity as well as by the signaling molecules abscisic acid and salicylic acid, indicating that ZmCOI6.1 is a stress-responsive gene. ZmCOI6.1 is alternatively spliced and yields two transcripts, the level of which change depending on the stress, indicating a possible mechanism of regulation at the splicing level. Constitutive expression of ZmCOI6.1 in Arabidopsis yielded plants that were less tolerant to abiotic stress, providing evidence that ZmCOI6.1 may be a negative regulator.
Abstract: Unfavourable environmental conditions such as cold induce the transcription of a range of genes in plants in order to acclimate to these growth conditions. To better understand the cold acclimation of maize (Zea mays L.) it is important to identify components of the cold stress response. For this purpose, cold-induced genes were analysed using the PCR-select cDNA subtraction method. We identified several novel genes isolated from maize seedling exposed for 48h to 6 degrees C. Of 18 Zea mays cold-induced genes (ZmCOI genes) characterized, the majority share similarities with proteins with known function in signal transduction and photosynthesis regulation. RT-PCR was conducted for a selected group of genes, namely ZmCOI6.1, ZmACA1, ZmDREB2A and ZmERF3, confirming the induction by low temperature. In addition, it was found that their expression was strongly induced by other abiotic stresses such as drought and high salt concentration, by stress signalling molecules such as jasmonic acid, salicylic acid and abscisic acid, and by membrane rigidification. These results suggest that this group of genes is involved in a general response to abiotic stresses.
Abstract: Transport of the viral genome into the nucleus is an obligatory step in the replication cycle of plant pararetro- and geminiviruses. In both these virus types, the multifunctional coat protein (CP) is thought to be involved in this process. Here, a green fluorescent protein tagging approach was used to demonstrate nuclear import of the CPs of Rice tungro bacilliform virus (RTBV) and Mungbean yellow mosaic virus--Vigna (MYMV) in Nicotiana plumbaginifolia protoplasts. In both cases, at least two nuclear localization signals (NLSs) were identified and characterized. The NLSs of RTBV CP are located within both N- and C-terminal regions (residues 479KRPK/497KRK and 744KRK/758RRK), and those of MYMV CP within the N-terminal part (residues 3KR and 41KRRR). The MYMV and RTBV CP NLSs resemble classic mono- and bipartite NLSs, respectively. However, the N-terminal MYMV CP NLS and both RTBV CP NLSs show peculiarities in the number and position of basic residues. In vitro pull-down assays revealed interaction of RTBV and MYMV CPs with the nuclear import factor importin alpha, suggesting that both CPs are imported into the nucleus via an importin alpha-dependent pathway. The possibility that this pathway could serve for docking of virions to the nucleus is discussed.
Abstract: Using the yeast two-hybrid system, we show that the ORF III product of cauliflower mosaic virus (pIII) interacts through its C-terminus with the viral coat protein. The last five amino acids of pIII were essential for the interaction and virus infectivity. Deletion of the last three amino acids or the mutation F129A decreased the strength of the interaction by 90%. We further show that pIII is closely associated with virus particles found in the inclusion bodies of infected plants but not in viral particles released from the inclusion bodies by urea treatment.
Abstract: Using the yeast three-hybrid system, the interaction of the Cauliflower mosaic virus (CaMV) pregenomic 35S RNA (pgRNA) leader with the viral coat protein, its precursor, and a series of derivatives was studied. The purine-rich domain in the center of the pgRNA leader was found to specifically interact with the coat protein. The zinc finger motif of the coat protein and the preceding basic domain were essential for this interaction. Removal of the N-terminal portion of the basic domain led to loss of specificity but did not affect the strength of the interaction. Mutations of the zinc finger motif abolished not only the interaction with the RNA but also viral infectivity. In the presence of the very acidic C-terminal domain, which is part of the preprotein but is not present in the mature CP, the interaction with the RNA was undetectable.
Abstract: Rice tungro bacilliform virus (RTBV) is a plant pararetrovirus whose DNA genome contains four genes encoding three proteins and a large polyprotein. The function of most of the viral proteins is still unknown. To investigate the role of the gene II product (P2), we searched for interactions between this protein and other RTBV proteins. P2 was shown to interact with the coat protein (CP) domain of the viral gene III polyprotein (P3) both in the yeast two-hybrid system and in vitro. Domains involved in the P2-CP association have been identified and mapped on both proteins. To determine the importance of this interaction for viral multiplication, the infectivity of RTBV gene II mutants was investigated by agroinoculation of rice plants. The results showed that virus viability correlates with the ability of P2 to interact with the CP domain of P3. This study suggests that P2 could participate in RTBV capsid assembly.
Abstract: The tomato yellow leaf curl virus (TYLCV) causes major yield losses in tomato production in many tropical and subtropical regions. Therefore, there is an increased need to apply molecular methods for the detection and characterization of the main TYLCV isolates that affect Cuban tomato plantations. A DNA fragment containing the gene encoding the coat protein of a Cuban TYLCV isolate was amplified by polymerase chain reaction (PCR). DNA hybridization with specific radiolabeled probes corroborated the identity of the amplified product, and allowed to analyze the integration into a full-length TYLCV genome. The threshold of TYLCV detection by PCR in plants and viruliferous whiteflies was within the reported range. To detect TYLCV infections, samples collected from tomato plantations of several regions in Cuba were analyzed by PCR. The amplified coat protein gene was also effectively used as a DNA probe in Dot blot assays to detect geminivirus in plants.
