Expression of yeast Hem1 controlled by Arabidopsis HemA1 promoter enhances leaf photosynthesis in transgenic tobacco

Abstract

A gene encoding aminolevulinate synthase (ALA-S) in yeast (Saccharomyces cerevisiae YHem1) was introduced into the genome of tobacco (Nicoliana tabacum) under the control of Arabidopsis thaliana HemA1 gene promoter (AtHemA1 P). All transgenic lines transcribed the YHem1 gene, especially under light condition. The capacity to synthesize ALA and therefore chlorophyll was increased in transformed plants. Determination of gas exchange suggested that transgenic plants had significantly higher level of net photosynthetic rate (P ( n )), stomatal conductance (G ( s )) and transpiration rate (T ( r )), compared to the wild type (WT). Analysis with a modulated chlorophyll fluorometer demonstrated that the genetic transformation also caused a significant increase in photochemical efficiency of PSII ([Formula: see text]), actual photochemical efficiency (Ф ( PSII )), photochemical quenching (qP), electron transfer rate (ETR) and the energy proportion in photochemistry (Pc), but decrease in proportion in heat dissipation (Hd). Chlorophyll-a fast fluorescence measurement and JIP-test indicated that photosynthetic performance index on cross section basis (PI ( CS )) and electron transport flux (ET ( o ) /CS) of transgenic tobacco were increased remarkably. And the probability that a trapped exciton can move a electron into the electron transport chain beyond Q ( A ) (-) (Ψ ( o )) and the density of active reaction centers (RC/CS) were also increased obviously in transgenic tobacco. These results imply that transgenic tobacco plants expressing YHem1 gene had higher photosynthetic capacity and energy conversion efficiency than the WT plants.

Study on salt tolerance with YHem1 transgenic canola (Brassica napus)

“…As seed yield is more important than shoot or root growth for many crops, it can be deduced that YHem1 is a useful gene which can be used to breed new plants with stronger salt tolerance. In fact, yearly field experiments have shown that the YHem1 transgenic canola possesses much greater productivity than the WT (unpublished), which is in agreement with the results in Table and in tobacco (Zhang et al ).…”

“…The transgenic canola ( B. napus ) used in this work was obtained from a previous study (Zhang ), which contained a constituted binary gene YHem1 , i.e. yeast Hem1 gene controlled by Arabidopsis HemA1 gene promoter (Zhang et al , ). Polymerase chain reaction (PCR) analysis demonstrated that the constituted gene had been transformed into the genome of canola.…”

“…The assay of ALAS (EC 2.3.1.37) activity was conducted with the method described previously (Zhang et al ). Leaves of transgenic canola were homogenized in 20 mmol L −1 of phosphate buffer (pH 7.6) containing 330 mmol L −1 of sorbitol.…”

“…To evaluate ALA metabolism, the detached leaves were incubated in 20 mmol L −1 of LA for 3 h at dark and then exposed to PPFD of 80 µmol m −2 s −1 for 6 h. After induction, the tissues were extracted in acetic acid buffer and 5‐ALA content was quantified as described above. The 5‐ALA content measured in LA‐induced leaves represented the synthesizing ability because its catabolism was blocked, and the difference between LA induction and non‐LA induction was the catabolism of 5‐ALA (Zhang et al , ).…”

“…In our laboratory, Zhang et al () constructed a binary vector pYK3840‐YHem1 that contains a Hem1 gene from yeast and a light‐responsive promoter of HemA1 gene ( AtHemA1 ) from Arabidopsis thaliana (McCormac et al ). When the YHem1 gene was transformed into genome of tobacco, the transgenic plants exhibited higher ability of photosynthesis and photochemistry, and more importantly, they grew well under natural solar light (about 2000 µmol m −2 s −1 ) without any photobleaching symptom (Zhang et al ). In the transgenic Arabidopsis (Zhang et al ) or tomato (Li et al ) with the constituted YHem1 , the plants grew much better than the WT, suggesting that the transgenic plants improved their salt tolerance.…”