By Lukas Herwig, Checkbiotech

A highly specialized molecule that responds to light, called a photoreceptor, provides new plant architecture and increases grain yield.

Translucent white grains with a great aroma – these are the well-known characteristics of Basmati rice that renders this rice so attractive for global agricultural markets.

However, yields are reduced by other traits of Basmati rice. For example, a tall stature and a weak stem are among the traits that trigger low yields. Yet, genetic engineering could solve this issue. This is exactly what a research group at Cornell University did.

Recently, researchers of the Department of Molecular Biology and Genetics at Cornell University published their work in the Journal Planta. They reported on how they were able to increase the production of Arabidopsis thaliana PHYTOCHROME A (PHYA), which led to an increase in grain yield in a rice variety called Pusa Basmati-1 rice.

The PHYA gene that they studied encodes a photoreceptor belonging to the phytochromes, a family of molecules absorbing light in the range of red to far-red. When light hits the PHYA photoreceptor, it induces a structural change in PHYA, which triggers an intercellular signal called a signal-transduction.

The team generated transgenic Pusa Basmati-1 rice seedlings containing the Phytochrome A gene - the photoreceptor - of Arabidopsis thaliana, a plant common in research. The main effect of increase the production PHYA has been observed by the research group in several experiments. For example, in experiments with tomatoes, a phenomenon called dwarfing occurred, where the overall stature of the tomato plant was reduced. In addition, by increasing the production of PHYA, the adult tomato plants grew bushier and increased their branching.

Although the complete mode of action of PHYA is not understood, what is known is that this type of photoreceptor belongs to the phytochromes, a family of molecules absorbing light in the range of red to far-red. When light hits the PHYA photoreceptor, it induces a structural change in PHYA, which triggers an intercellular signal called a signal-transduction.

Dr. Ray Wu’s and his team believe that the alteration of this specific signal-transduction pathway somehow changes the resource partitioning - resulting in a higher grain yield - could be fulfilled.

Since hunger and poor agricultural conditions contribute a lot to today’s global issues, genetic engineering may help to solve such problems. Dr. Ray Wu and his research group believe that if they are able to extend their observations to other rice varieties this could provide high yielding, semi-dwarf plants that can be used as donors in breeding programs.

Lukas Herwig is studying biology at University of Basel and is a Science Writer for Checkbiotech.
Contact him at l.herwig@stud.unibas.ch.

Journal Planta (2005)

Contact:
A. K. Garg & R. J. Wu
Department of Molecular Biology and Genetics,
Cornell University, Ithaca, New York 14853, USA
E-mail: ray.wu@cornell.edu
Tel.: +1-607-2555710
Fax: +1-607-2552428

ORIGINAL ARTICLE
Light-regulated overexpression of an Arabidopsis phytochrome A gene in rice alters plant architecture and increases grain yield
Ajay K. Garg, Ruairidh J. H. Sawers, Haiyang Wang, Ju-Kon Kim, Joseph M. Walker, Thomas P. Brutnell, Mandayam V. Parthasarathy, Richard D. Vierstra and Ray J. Wu

^ABSTRACT

The phytochromes are a family of red/far-red light absorbing photoreceptors that control plant developmental and metabolic processes in response to changes in the light environment. We report here the overexpression of Arabidopsis thaliana PHYTOCHROME A (PHYA) gene in a commercially important indica rice variety (Oryza sativa L. Pusa Basmati-1). The expression of the transgene was driven by the light-regulated and tissue-specific rice rbcS promoter. Several independent homozygous sixth generation (T₅) transgenic lines were characterized and shown to accumulate relatively high levels of PHYA protein in the light. Under both far-red and red light, PHYA-overexpressing lines showed inhibition of the coleoptile extension in comparison to non-transgenic seedlings. Furthermore, compared with non-transgenic rice plants, mature transgenic plants showed significant reduction in plant height, internode length and internode diameter (including differences in cell size and number), and produced an increased number of panicles per plant. Under greenhouse conditions, rice grain yield was 6–21% higher in three PHYA-overexpressing lines than in non-transgenic plants. These results demonstrate the potential of manipulating light signal-transduction pathways to minimize the problems of lodging in basmati/aromatic rice and to enhance grain productivity.