Genetic & Molecular Analysis of the Regulation of Tropic Growth in Arabidopsis thaliana

University Of Missouri-Columbia, Columbia MO

Investigators

Abstract

The goal of this research is to understand how plants perceive changes in their environment, transduce that information and ultimately alter growth and/or development to elicit proper adaptive differential growth responses. The phototropic response is being used as a model system to study light-driven signal transduction and regulation of cellular growth. Several loci, previously identified via mutation, have been characterized as necessary for normal phototropism in Arabidopsis thaliana L. Heynh. The NPH4 locus (nonphototropic hypocotyl 4) is important not only for phototropism, but also for several additional differential growth responses, including gravitropism, apical hook maintenance and abaxial/adaxial leaf blade expansion. The NPH4 gene has been cloned and found to encode the auxin-regulated transcriptional activator, ARF7, suggesting that auxin-dependent changes in gene transcription are prerequisite for proper organ bending responses. However, NPH4/ARF7 is not the sole regulator of these changes since the phenotypes of nph4-null mutants are conditional. For example, phytochrome A (phy A) activation, which leads to enhancement of blue light-induced phototropism in wild-type, results in restoration of a partial phototropic response in nph4 seedlings. Specific aims are 1) To identify genes that are transcriptionally regulated by NPH4/ARF7 and necessary for tropic reponsiveness and 2) To characterize components of the phytochrome A-dependent modulatory pathway(s) leading to phototropic enhancement. Because of their sessile nature, plants have evolved movement strategies that involve organ bending in order to respond to changes in their environment. Dramatic, rapid and reversible changes in morphology can result from differential growth- or unequal cellular growth in one position of an organ relative to an opposing position. Continued study of the nph4 mutants and in planta function of the NPH4/ARF7 protein will provide significant new insights into the basic cellular mechanisms leading to tropic responses, as well as the interactions between multiple signal-response pathways that modulate those tropic responses.