Blue Light Regulates Adventitious Root Growth Through Modulating PIN3-mediated Auxin Distribution In Arabidopsis

Root,as one of the important organs of higher plants,can absorb water and nutrients to maintain plant normal life activities,thus,the development of the root system directly affects the growth of the whole plant.Plant root are divided into primary roots,lateral roots and adventitious roots.Adventitious roots not only expand plant's root system,but also enables the regeneration of plants and cells.This phenomenon makes it widely used in plant organ cutting and tissue culture.Therefore,studying the molecular mechanism underlying plant adventitious roots growth and development is of great importantance.Auxin plays a key role in regulating root grwoth and development.Previous studies have shown that there is a concentration gradient of auxin in plant root tip,which affecting the fate of the root cells.This auxin distribution in root not only depends on auxin biosynthesis,but also auxin polar transport,where the auxin efflux carriers play a crucial role.Light also plays a vital role in the regulation of plant growth and development.It is not only energy source for plant photosynthesis,but also an important environmental factor that regulates plant development.Lights with different wavelengths sensed by plant different photoreceptors,affects plant architecture by modulating auxin accumulation and distribution.But,whether and how light regulates plant adventitious root formation through changes of auxin accumulation remains unclear.This study found that blue light can obviously induce the formation of plant adventitious roots.The main research results obtained through in-depth analysis and research are as follows:1.We assayed the adventitious root formation in hypocotyle of wild-type Arabidopsis plants under different light treatments including white light,blue light,red light,far-red light and darkness.Our results showed that the density of adventitious roots in plant hypocotyles treated with blue light was significantly higher than that in plants treated with white light,red light or far red light,indicating that blue light induces plant adventitious root in hypocotyle.2.We examined the formation of adventitious root in photoreceptor mutants inculding photl,phot2,photl phot2,cryl and nph3 under blue light.We found that the adventitious roots density of phot1 phot2 and nph3 was significantly lower than that of wild type and other photoreceptor mutants under blue light,revealing that PHOT1,PHOT2 and NPH3 are involved in blue light-indcued development of plant adventitious roots.3.It was reported that auxin affects the development of plant adventitious roots.Our results showed that treatment with the auxin transport inhibitor 1-N-naphthylphthalamic acid(NPA)can significantly repressed blue light-induced plant adventitious root.Further study showed that the adventitious root density of auxin efllux carrier mutant,pin3 was significantly lower than that of the wild type under blue light,indicating that PIN3 is involved in blue light-induced adventitious root formation.4.Previous studies showed that photoreceptor PHOT1 regulates plant architecture by interacting with NPH3.a vital factor in blue light signaling pathway To investigate whether PIN3 acts downstream of NPH3 in blue light-induced adventitious root,we performed yeast two-hybrid and BiFC experiments,and our results showed that NPH3 can interact with PIN3.These data suggest that PIN3 is likely a downstream player in NPH3-mediated blue light-induced adventitious root.5.To know that effect of NPH3 in PIN3 protein level,we assayed PIN3 accumulation in hypocotyle using PIN3::PIN3-GFP transgenic plants,and found that PIN3 protein level was higher in plants treated with blue light than that with darkness especially in the pericycle.Further,we assessed PIN3 protein level in nph3 PIN3::PIAN3-GFP plant in hypocotyles,and found that blue light-induced PIN3 protein accumulation was significantly repressed in nph3 mutant,supporting that NPH3 functions in blue light-induced adventitious root by affecting PIN3 protein accumulation.6.Blue light may affect auxin distribution or accumulation by regulating PIN3 accumulation in the process of adventitious root formation,thus,we assayed the GUS enzymatic activity of DR5::GUS transgenic plant,a widely-used reporter system to study auxin response.Our results showed that blue light can significantly induce GUS enzymatic activity compared with white light and darkness,suggesting that blue light promotes the accumulation of auxin.Then,we further detect the IAA levels in wild-type and phot1?phot2?photl phot2?nph3?cry1?pin3mutant plants under blue light,white light and darkness.Our results showed that blue light significantly induced the accumulation of IAA in the wild type compared with white light or darkness.Also,blue light-induced IAA accumulation was repressed in phot1?phot2?photl phot2?nph3?pin3 mutant,confirming that blue light functions in the formation of plant adventitious roots in hypocotyle by regulating auxin accumulation.