Given that plants are sessile by nature, the ability to respond to light cues play a critical role in development. Phototropins have been known to be an important player in the blue-light response: regulating phototropism, chloroplast migration, and stomatal opening. 

Interestingly, work from our labs have shown a role for the phototropins in directing root growth downward in response to light gradients just beneath the soil and promotes drought tolerance. To further understand this process, studies from our labs have focused on how a gain of function phot1 allele; hyper phototrophic hypocotyl (hph) could inform us regarding the possible enhancement of the drought tolerance response. Hph enhances hypocotyl curvature of plants during the second phototropic response and is conferred by one copy of a full-length version of phototropin 1 (phot1), and a truncated version of the same photoreceptor.  To circumvent the difficulties of working with a segregating population, stable double transgenic recapitulation lines have been created to recapitulate the hph phenotype. We have employed the use of these transgenic recapitulation lines and tested them in both well watered and water deficient conditions in the green house.  Because we were interested in the amount of biomass generated, these experiments were done in conetainers using a 1: 1: 2 ratio of fritted clay, coarse sand, and soil-less growth media (Pro-Mix BX) with one plant per container.  After reaching establishment, plants were put on the following watering schedule: well-watered plants were bottom watered (ie-soaked) for 1 hour every other day and dry treated plants were bottom watered for 1 hour every fifth day. These lines were evaluated for fecundity, date to bolt and date to flower, biomass production and additional growth parameters.

Results/Conclusions

A preliminary study suggested that the naturally occurring, segregating population of hph is slightly more water use efficient that the Columbia ecotype.  Our green house analysis using transgenic recapitulation lines have been utilized to further investigate hph's affect on water use efficiency.  These recapitulation lines have been tested under well-watered and dry conditions and have been assayed for a number of parameters. Our preliminary results suggest that the hph phenotype gives rise to a number of pleiotropic effects- including effects on time to bolt, which is not surprising, given the number of roles phototropins play in plant growth and development.