How a simple chloroplast psbA gene mutation changed world agriculture

TL;DR

This paper explores how a single mutation in the chloroplast psbA gene of weeds led to resistant biotypes that significantly impacted global agriculture, revealing complex photosynthetic regulation and evolutionary dynamics.

Contribution

It uncovers the pleiotropic effects of a psbA gene mutation on plant physiology, photosynthesis, and weed resistance, linking molecular changes to agricultural practices and crop resistance evolution.

Findings

Resistant biotypes emerged from a single gene mutation.

Photosynthetic efficiency varies with environmental conditions.

Herbicide-resistant crops extended the evolution of resistant weeds.

Abstract

Atrazine as a weed control tactic profoundly changed world agriculture. Long-term use revealed resistant biotypes, R, with a single base pair mutation of the chloroplast psbA gene. The R phenotype emerged from a sequential cascade of pleiotropic effects from the plastid to the whole plant. This reorganization of the R biotype revealed photosynthetic regulation at different levels of plant organization. The environment affected R plant productivity differently than in the susceptible, S, biotype. A consistent, differential, pattern of photosynthesis was observed between R and S over the diurnal light period. Photosynthetic superiority of a biotype was a function of the time of day, plant age temperature. Under highly favorable environmental conditions S often had the advantage over R. Under less favorable, stressful, conditions R can be at an advantage over S. Pleiotropic reorganization revealed a sun-air-leaf Shannon communication system, providing insights into the complex interaction of chloroplast components in photosynthetic regulation. Altered plastid thylakoid and stomatal function regulate how the R leaf utilizes the sun-air environment. Movement of sun-air messages demonstrated how sunlight and air are modified to a usable message for carbon fixation. These insights showed how agriculture changed weed populations, and how resistant weed populations changed agriculture. These changes changed herbicide resistance: introduction of herbicide resistant crops, HRC. The development of HRCs extended the evolutionary reach of R weeds. R weed biotypes were naturally selected in these introduced HRCs: an evolutionary spiral of human technology extended the phenotypic reach of R biotypes.