Coinvolgimento del criptocromo nella risposta precoce di Arabidopsis al campo magnetico: analisi trascrizionale dei geni dipendenti dalla luce

Throughout Earth's history, the geomagnetic field (GMF) has always been a natural element of the environment. Its flux density is about 50 &#956;T at the Earth's surface, and during MF polarity reversals its intensity drops to zero. Joint analysis of the fossil record and paleomagnetic data have pointed out a correlation between fossil pattern of extinction, speciation and GMF polarity reversals. In particular, periods of normal polarity transitions overlapped with the diversification of most of the familial Angiosperm lineages. Nowadays, it is strongly argued that MF has direct effects on plants. However, the nature of the plant magnetoreceptor is still unclear. The radical pair mechanism seems to be the most reliable theory of biochemical responses to MF, and the blue-light photoreceptor cryptochrome has been suggested as a plant magnetoreceptor. In particular, in Arabidopsis, MF intensity affects cryptochrome-dependent growth responses, but in a contradictory and irreproducible way. Moreover, changes at the transcription levels of cryptochrome signaling cascade genes have been rarely investigated under different MF conditions. The aim of this work was to investigate the possible correlation between Arabidopsis wild-type and Cry1/Cry2 double mutant mutant early responses to MF and cryptochrome activity, using different light conditions. Arabidopsis WT and Cry1/Cry2 seedlings were exposed to near null MF (NNMF, < 40 nT) and GMF control conditions for 72 h, using long-day white light, continuous white light, continuous blue light, continuous red light and continuous darkness conditions. Root and shoot length was analyzed and correlated to the quantitative expression of 14 genes involved in cryptochrome signaling cascade and other photo-responses to different wavelengths. From a morphological point of view and despite the light treatment, NNMMF did not change plant photomorfogenic responses. However, MF intensity strongly influenced the expression of light-dependent genes in all light conditions. Under photo-activated cryptochrome condition (continuous blue-light, continuous and long-day white-light), NNMF caused a significant regulation of FKF1-LKP2 blue-photoreceptors and HY5, HYH, CO, PIF3 and PKS1 transcription factors, related to both cryptochrome and phytochrome activity. Moreover, under blue-light and long day white-light conditions, deficiency of functional CRYs under NNMF defined a global transcription shutdown, therefore corroborating the role of activated cryptochrome in magnetoreception. Under red-light condition, in response to NNMF, a strong regulation of FKF1, LKP2, PIF3 and PKS1 occurred in the whole plant, with differences in modulation between WT and Cry1/Cry2 mutant. Transcriptional analyses suggest that other light-related magnetoreceptors could work under red-light exposition and cryptochrome could act only downstream to the MF signal reception. NDPK2 regulation in darkness emphasized a light-independent mechanism of MF reception in the roots. It appears evident that the light-independent response to MF could be related to other signals such as oxidative response and/or Ca2+ signaling. Moreover, oxidative response was induced by NNMF in all light conditions and it influenced the expression of ANS and CHS, involved in anthocyanin biosynthesis.