Nitrate application affects root morphology by altering hormonal status and gene expression patterns in B9 apple rootstock nursery plants

Lateral roots(LRs)are critical for absorbing water,minerals,and nutrients.Nitrate is a vital signaling molecule for regulating LR growth.However,understanding how nitrate interacts with endogenous hormones and genes to coordinate LR development is a bottleneck.In this study,B9 apple rootstock nursery plants were cultured hydroponically and treated with different nitrate treatments(Control;T1,2.25 mM L^(−1);T2,9 mM L^(−1);T3,18 mM L^(−1);T4,36 mM L^(−1);and T5,72 mM L^(−1)),where T5 outperformed the other treatments.Nursery plants were subsequently treated with control and T5 to explore the underlying physiological and molecular mechanisms by which nitrate promoted LR growth.Plant height,stem diameter,root morphological parameters,endogenous hormones,and gene expression levels were measured.Results showed that T5 promoted LR growth by increasing the endogenous contents of indole-3-acetic acid(IAA)and gibberellic acid(GA),and by decreasing the contents of abscisic acid(ABA),jasmonic acid(JA),and zeatin riboside(ZR)at most time points.Furthermore,the relative expression levels of nitrate transporter genes were upregulated in the control group,and nitrate assimilation genes were upregulated in T5 nursery plants at various time points.In addition,the transcript abundances of auxin-related genes were higher in T5 nursery plants,which increased auxin contents.MdSHR,MdGATA1,and MdSCR1 expressions were induced,hence increasing LR growth.In contrast,higher auxin content raised MdWOX11 expression,which enhanced the MdLBD16 and MdLBD29 expression levels,thus prompting the transcripts of cell cycle-related genes:MdCYCD1;1 and MdCYCP4;1.Overall,the changes in hormonal content and gene expression levels followed superior LR growth by T5.

Identification of the HAK gene family reveals their critical response to potassium regulation during adventitious root formation in apple rootstock

Adventitious root formation is a bottleneck during vegetative proliferation.Potassium(K^(+))is an essential macronutrient for plants.K^(+)accumulation from the soil and its distribution to the different plant organs is mediated by K^(+)transporters named K^(+)transporter(KT),K^(+)uptake(KUP),or high-affinity K^(+)(HAK).This study aimed to identify members of the HAK gene family in apples and to characterize the effects of K^(+)supply on adventitious root formation and on the expression of HAK genes and the genes that putatively control auxin transport,signaling,and cell fate during adventitious root formation.In this study,34 HAK genes(MdHAKs)were identified in the apple(Malus×domestica‘Golden Delicious’)genome.A phylogenetic analysis divided MdHAKs into four clusters(Ⅰ,Ⅱ,Ⅲ,andⅣ),comprising 16,1,4,and 13 genes,respectively.The syntenic relationships revealed that 62.5%of the total MdHAK genes arise from genomic duplication events.Chromosome location,domain structure,motif analysis,and physico-chemical characteristics were subsequently investigated.Furthermore,the application of K^(+)indicated the emergence of adventitious roots at 8 d and produced more adventitious roots at 16 d than the K^(+)-free control(CK)treatment.In addition,various MdHAKs showed root-specific expression in B9 apple rootstock stem cuttings and enhanced expression during the initiation and emergence stages of adventitious root formation in response to K^(+)treatment.Additionally,K^(+)treatment enhanced the expression levels of MdPIN1,MdPIN2,and MdAUX1.Further data indicated that a higher expression of MdWOX11,MdLBD16,and MdLBD29 and of cell cycle-related genes contributed to the auxin-stimulated adventitious root formation in response to K^(+).