The nitrate-responsive transcription factor Md NLP7 regulates callus formation by modulating auxin response

Under appropriate culture conditions,plant cells can regenerate new organs or even whole plants.De novo organ regeneration is an excellent biological system,which usually requires additional growth regulators,including auxin and cytokinin.Nitrate is an essential nutrient element for plant vegetative and reproductive development.It has been reported that nitrate is involved in auxin biosynthesis and transport throughout the growth and development of plants.In this study,we demonstrated that the ectopic expression of the MdNLP7 transcription factor in Arabidopsis could regulate the regeneration of root explants.MdNLP7 mainly participated in the regulation of callus formation,starting with pericycle cell division,and mainly affected auxin distribution and accumulation in the regulation process.Moreover,MdNLP7 upregulated the expression of genes related to auxin biosynthesis and transport in the callus formation stage.The results demonstrated that MdNLP7 may play a role in the nitrate-modulated regeneration of root explants.Moreover,the results revealed that nitrate–auxin crosstalk is required for de novo callus initiation and clarified the mechanisms of organogenesis.

MdbHLH162 connects the gibberellin and jasmonic acid signals to regulate anthocyanin biosynthesis in apple

Anthocyanins are secondary metabolites induced by environmental stimuli and developmental signals.The positive regulators of anthocyanin biosynthesis have been reported,whereas the anthocyanin repressors have been neglected.Although the signal transduction pathways of gibberellin(GA)and jasmonic acid(JA)and their regulation of anthocyanin biosynthesis have been investigated,the cross-talk between GA and JA and the antagonistic mechanism of regulating anthocyanin biosynthesis remain to be investigated.In this study,we identified the anthocyanin repressor MdbHLH162 in apple and revealed its molecular mechanism of regulating anthocyanin biosynthesis by integrating the GA and JA signals.MdbHLH162 exerted passive repression by interacting with MdbHLH3 and MdbHLH33,which are two recognized positive regulators of anthocyanin biosynthesis.MdbHLH162 negatively regulated anthocyanin biosynthesis by disrupting the formation of the anthocyanin-activated MdMYB1-MdbHLH3/33complexes and weakening transcriptional activation of the anthocyanin biosynthetic genes MdDFR and MdUF3GT by MdbHLH3 and MdbHLH33.The GA repressor MdRGL2a antagonized MdbHLH162-mediated inhibition of anthocyanins by sequestering MdbHLH162 from the MdbHLH162-MdbHLH3/33 complex.The JA repressors MdJAZ1 and MdJAZ2 interfered with the antagonistic regulation of MdbHLH162 by MdRGL2a by titrating the formation of the MdRGL2a-MdbHLH162 complex.Our findings reveal that MdbHLH162 integrates the GA and JA signals to negatively regulate anthocyanin biosynthesis.This study provides new information for discovering more anthocyanin biosynthesis repressors and explores the cross-talk between hormone signals.

Apple SINA11-JAZ2 module is involved in jasmonate signaling response

Jasmonic acid(JA)is an important phytolipid hormone involved in regulating many processes of plant growth and development,and plays a key role in plant resistance to biotic and abiotic stresses.Since the first discovery of methyl jasmonate(MeJA)from jasminum in 1962,the JA signaling pathway have been dissected.