PLANT RESPONSE TO MAGNESIUM AVAILABILITY: ROOT MORPHOLOGY ADAPTATION AND INVESTIGATION OF A ROLE FOR THE CLOCK

Abstract

Understanding the dynamical bases of the interaction between the plant mineral nutrition and the circadian clock could contribute to improve crop yield and resistance to adverse conditions, such as mineral element deficiencies. Magnesium is an essential element that catalyzes more than six hundred enzymatic reactions and occupies the center of the chlorophyll structure in plants. Physiological targets of magnesium deficiency are generally better described in aerial than in belowground organs. In this thesis, we first characterized the root morphology of the model species Arabidopsis thaliana (Columbia-0) in response to magnesium supply during in vitro culture. The length of primary root and the number and length of lateral roots decreased during magnesium depletion. A local magnesium-rich source does not enhance the root foraging capacity, unlike some other major nutrients. Auxin and abscisic acid emerged as two hormones shaping root morphology in response to magnesium deficiency. Second, we investigated the natural variation of the root morphology response to magnesium supply in Arabidopsis. Thirty-six accessions were screened in vitro. Compared to the reference Columbia-0, some accessions had higher number and length of lateral roots at low magnesium supply. Root or shoot magnesium concentrations did not implicitly correlate with the root morphological traits. However, shoot calcium and root phosphorus concentrations correlated positively with the lateral root number and length, while root iron negatively with the length of primary root. Third, we focused on the interaction between the plant magnesium nutrition and the circadian clock circuit. We tested for a possible involvement of PHYTOCHROME INTERACTING FACTOR 3-LIKE 1 (PIL1) - a clock-associated gene that is down-regulated during magnesium depletion - in morphological and physiological responses, and for a circadian connection of PIL1 in the context of magnesium deficiency. The phenotypes of loss-of-function and overexpression lines did not reveal a major role of PIL1 in the magnesium deficiency symptom manifestation but rather in the plant mineral profile. The expression of PIL1 was apparently not under any circadian control. However, PIL1 seemed to regulate the expressions of some core clock genes (CCA1, LHY and PRR9), which were also targets during magnesium deficiency. In conclusion, PIL1 has a link with the circadian rhythm machinery but it does not emerge as a pivotal regulator of magnesium stress responses.Doctorat en Sciencesinfo:eu-repo/semantics/nonPublishe