Chimeric promoter mediates guard cell-specific gene expression in tobacco under water deficit.

The engineering of stomatal activity under water deficit through guard cell-specific gene regulation is an effective approach to improve drought tolerance of crops but it requires an appropriate promoter(s) inducible by water deficit in guard cells. We report that a chimeric promoter can induce guard cell-specific gene expression under water deficit. A chimeric promoter, p4xKST82-rd29B, was constructed using a tetramer of the 82 bp guard cell-specific regulatory region of potato KST1 promoter (4xKST82) and Arabidopsis dehydration-responsive rd29B promoter. Transgenic tobacco plants carrying p4xKST82-rd29B:mGFP-GUS exhibited GUS expression in response to water deficit. GUS enzyme activity of p4xKST82-rd29B:mGFP-GUS transgenic plants increased ~300 % by polyethylene glycol treatment compared to that of control plant but not by abscisic acid (ABA), indicating that the p4xKST82-rd29B chimeric promoter can be used to induce the guard cell-specific expression of genes of interest in response to water deficit in an ABA-independent manner.

A putative tomato inositol polyphosphate 5-phosphatase, Le5PT1, is involved in plant growth and abiotic stress responses.

Based on sequence similarity to Arabidopsis inositol polyphosphate 5-phosphatases (5PTases) involved in abiotic stress responses and development, four tomato cDNAs (Le5PT1-4) encoding putative 5PTase proteins were identified. The predicted protein sequences of the Le5PTs include conserved catalytic domains required for 5PTase enzyme activity. Le5PT1, 2, and 3 showed high amino acid sequence identity with At5PTase2, At5PTase1 and At5PTase3, and At5PTase5 and At5PTase6, respectively. The expression of Le5PT1 was downregulated soon after initiation of dehydration and salt stress as well as exposure to polyethylene glycol (PEG) and NaCl, but not by exogenous ABA treatment. On the other hand, the expression of Le5PT2 gradually increased with time in all treatments. Transgenic tobacco plants overexpressing Le5PT1 exhibited reduced growth in height, leaf area, and dry weight compared to wild type plants. Transgenic plants also had lower water use efficiency (WUE) than wild type and the downregulation of the drought-responsive gene, NtERD10B. Together these results suggest that Le5PT1 may have a negative role in response to water deficit through the repression of drought-inducible genes that in turn affects plant growth and development.

Effects of vermicomposts produced from food waste on the growth and yields of greenhouse peppers.

Vermicomposts, produced commercially from food wastes, were substituted at a range of different concentrations into a soil-less commercial bedding plant container medium, Metro-Mix 360 (MM360), to evaluate their effects on the growth and yields of peppers in the greenhouse. Six-week-old peppers (Capsicum annum L. var. California) were transplanted into 100%, 80%, 60%, 40%, 20% or 10% MM360 substituted with 0%, 10%, 20%, 40%, 60%, 80% and 100% vermicompost. All plants were watered three times weekly with 200 ppm Peter's Nutrient Solution from the time of transplanting up to 107 days. Peppers grown in potting mixtures containing 40% food waste vermicomposts and 60% MM360 yielded 45% more fruit weights and had 17% greater mean number of fruits than those grown in MM360 only. The mean heights, numbers of buds and numbers of flowers of peppers grown in potting mixtures containing 10-80% vermicompost although greater did not differ significantly from those of peppers grown in MM360. There were no positive correlations between the increases in pepper yields, and the amounts of mineral-N and microbial biomass-N in the potting mixtures, or the concentrations of nitrogen in the shoot tissues of peppers. Factors such as: an improvement of the physical structure of the potting medium, increases in populations of beneficial microorganisms and the potential availability of plant growth-influencing-substances produced by microorganisms in vermicomposts, could have contributed to the increased pepper yields obtained.

Phytochromes A1 and B1 have distinct functions in the photoperiodic control of flowering in the obligate long-day plant Nicotiana sylvestris.

The obligate long-day plant Nicotiana sylvestris with a nominal critical day length of 12 h was used to dissect the roles of two major phytochromes (phyA1 and phyB1) in the photoperiodic control of flowering using transgenic plants under-expressing PHYA1 (SUA2), over-expressing PHYB1 (SOB36), or cosuppressing the PHYB1 gene (SCB35). When tungsten filament lamps were used to extend an 8 h main photoperiod, SCB35 and SOB36 flowered earlier and later, respectively, than wild-type plants, while flowering was greatly delayed in SUA2. These results are consistent with those obtained with other long-day plants in that phyB has a negative role in the control of flowering, while phyA is required for sensing day-length extensions. However, evidence was obtained for a positive role for PHYB1 in the control of flowering. Firstly, transgenic plants under-expressing both PHYA1 and PHYB1 exhibited extreme insensitivity to day-length extensions. Secondly, flowering in SCB35 was completely repressed under 8 h extensions with far-red-deficient light from fluorescent lamps. This indicates that the dual requirement for both far-red and red for maximum floral induction is mediated by an interaction between phyA1 and phyB1. In addition, a diurnal periodicity to the sensitivity of both negative and positive light signals was observed. This is consistent with existing models in which photoperiodic time measurement is not based on the actual measurement of the duration of either the light or dark period, but rather the coincidence of endogenous rhythms of sensitivity - both positive and negative - and the presence of light cues.