Increased Phytochrome B Alleviates Density Effects on Tuber Yield of Field Potato Crops

Abstract

The possibility that reduced photomorphogenic responses could increase field crop yield has been suggested often, but experimental support is still lacking. Here, we report that ectopic expression of the Arabidopsis PHYB (phytochrome B) gene, a photoreceptor involved in detecting red to far-red light ratio associated with plant density, can increase tuber yield in field-grown transgenic potato (Solanum tuberosum) crops. Surprisingly, this effect was larger at very high densities, despite the intense reduction in the red to far-red light ratios and the concomitant narrowed differences in active phytochrome B levels between wild type and transgenics at these densities. Increased PHYB expression not only altered the ability of plants to respond to light signals, but they also modified the light environment itself. This combination resulted in larger effects of enhanced PHYB expression on tuber number and crop photosynthesis at high planting densities. The PHYB transgenics showed higher maximum photosynthesis in leaves of all strata of the canopy, and this effect was largely due to increased leaf stomatal conductance. We propose that enhanced PHYB expression could be used in breeding programs to shift optimum planting densities to higher levels.The world population is predicted to reach 8 billion by 2025, and this, in combination with current trends in dietary composition, will result in a substantial increase of food demand. The ability to satisfy this demand will rely heavily on the genetic improvement of cultivated plants to increase yield potentials and/or yield stability (i.e. the constancy of performance; Khush, 2001). Although yield per unit area continues to increase for many crops, maximum yield is not showing such an obvious trend, and this has been interpreted as a result of yield potential approaching a ceiling, whereas yield stability continues to grow (Mann, 1999). Although some consider that this ceiling represents the highest physically attainable yield (Sinclair, 1993), others are more confident that incorporation of the current wealth of knowledge in plant biology will overcome the decreasing rate of increase in yield potential. However, genetic modifications that appear beneficial when analyzed at the cellular or plant level do not necessarily translate into higher yields in the field, either because of negative side effects or simply because they do not operate on the limitations under field conditions.As incident solar radiation penetrates the canopy of commercial crops, it suffers a gradual attenuation of the photosynthetic photon flux density (PPFD) and of the red (R) to far-red (FR) ratio (Holmes and Smith, 1977). Changes in the R to FR ratio perceived by phytochromes initiate a number of responses such as increased stem extension growth (Morgan and Smith, 1976), reduced branching (Deregibus et al., 1983), and accelerated leaf senescence (Rousseaux et al., 1999), which are collectively called the shade avoidance syndrome (Smith, 2000). In growing canopies, some of these changes anticipate com...

Phytochrome B Represses Teosinte Branched1 Expression and Induces Sorghum Axillary Bud Outgrowth in Response to Light Signals

“…The sorghum ubiquitin gene (SbUBQ) was used as a loading control. Transgenic potato (Solanum tuberosum) plants overexpressing phyB produced more branches at high plant density (Boccalandro et al, 2003). These results are consistent with the hypothesis that active phyB suppresses accumulation of the TB1 mRNA, thereby promoting bud outgrowth.…”

The Art of Being Flexible: How to Escape from Shade, Salt, and Drought

“…This phenomenon is intensified by the presence of weeds that further enrich the crops with FR through FR reflection. Although many modern crops are semidwarf varieties, they still show FR-or high density-induced responses, such as stem elongation in maize (Zea mays; Dubois et al, 2010) and potato (Solanum tuberosum; Boccalandro et al, 2003), reduced tillering in wheat (Triticum aestivum; Ugarte et al, 2010), and reduced tuber growth in potato (Boccalandro et al, 2003). All these responses reduce crop yield.…”

“…Likewise, natural populations of Impatiens capensis become more sensitive to drought when expressing shade avoidance responses as compared with less shadeavoiding populations, presumably through reduced root investments in shade-avoiding plants (Huber et al, 2004). Although there have been studies showing yield suppression by low R:FR exposure in crops (Boccalandro et al, 2003;Ugarte et al, 2010), these have not considered light quality-induced suppression of root growth.…”

Overexpression of the phytochrome B gene from Arabidopsis thaliana increases plant growth and yield of cotton (Gossypium hirsutum)

“…A lot of work has been done on transformation of PHYB in potato (Thiele et al, 1999;Boccalendo et al, 2003;Schittenhelm et al, 2004), tomato (Said et al, 2007), and Arabidopsis (Wagner et al, 1991). The present investigation was carried out in cotton to determine the effect of overexpression of Arabidopsis thaliana PHYB gene on cotton growth and yield.…”