Molecular Insights Into Characterizing Temperature Effects On Growth and Development.

Quantitative inquiries into temperature effects on growth and development date to at least 1735 and the work of Reaumur that led to the concept of degree days.  Although extended by voluminous subsequent research, the causes underlying observed temperature responses long remained obscure.  The often close resemblance between organism-level temperature reaction norms and chemical kinetic activity curves plus the taxonomically broad incidence of these responses (e.g. in both plants and insects) strongly suggested molecular causes.  An overview of molecular mechanisms reveals ample opportunities for temperature effects to manifest themselves.  These range from simple temperature threshold detectors and diurnal clock temperature compensation circuitry in bacteria to studies of protein thermal stability and/or misfolding and their interactions with cellular quality control mechanisms.  One high end computing project is evaluating the thermal stabilities of approximately 22,000 variants of ca. 1500 primary metabolic proteins in 170 fully sequenced Arabidopsis ecotypes. In a much more focused molecular context, a particular histone complex serving as a scaffold for DNA coiling mediates some temperature responses.

Given the ubiquity and diversity of temperature-related molecular mechanisms plus the effectiveness of evolution at finding ways to increase fitness, it is not surprising that thermal effects ramify and interact throughout physiology in many subtle ways.  Specific examples range from modifications in clock frequency to nonlinear effects on photoperiod responses.  Moreover, there is mounting evidence that such effects are subject to local adaptation and possible evolutionary lags, thus increasing the complexity of landscape-scale prediction.  However, insights learned at the gene network level for some traits like flowering time may point toward more generic modeling strategies.  Recent work is presented describing integration of multiple information pathways driving redundant floral initiation switches.  More progress in this direction will be necessary to be successful at predicting plant responses under altered, non-analog climates.