N-MYC down-regulated-like proteins regulate meristem initiation by modulating auxin transport and MAX2 expression.
BACKGROUND
N-MYC down-regulated-like (NDL) proteins interact with the Gβ subunit (AGB1) of the heterotrimeric G protein complex and play an important role in AGB1-dependent regulation of lateral root formation by affecting root auxin transport, auxin gradients and the steady-state levels of mRNA encoding the PIN-FORMED 2 and AUXIN 1 auxin transport facilitators. Auxin transport in aerial tissue follows different paths and utilizes different transporters than in roots; therefore, in the present study, we analyzed whether NDL proteins play an important role in AGB1-dependent, auxin-mediated meristem development.


RESULTS
Expression levels of NDL gene family members need to be tightly regulated, and altered expression (both over-expression and down-regulation) confers ectopic growth. Over-expression of NDL1 disrupts vegetative and reproductive organ development. Reduced expression of the NDL gene family members results in asymmetric leaf emergence, twinning of rosette leaves, defects in leaf formation, and abnormal silique distribution. Reduced expression of the NDL genes in the agb1-2 (null allele) mutant rescues some of the abnormal phenotypes, such as silique morphology, silique distribution, and peduncle angle, suggesting that proper levels of NDL proteins are maintained by AGB1. We found that all of these abnormal aerial phenotypes due to altered NDL expression were associated with increases in basipetal auxin transport, altered auxin maxima and altered MAX2 expression within the inflorescence stem.


CONCLUSIONS
NDL proteins, together with AGB1, act as positive regulators of meristem initiation and branching. AGB1 and NDL1 positively regulate basipetal inflorescence auxin transport and modulate MAX2 expression in shoots, which in turn regulates organ and lateral meristem formation by the establishment and maintenance of auxin gradients.
Department of Botany, University of Delhi, Delhi, India.
Yashwanti
Y
Mudgil
Sanjay
S
Ghawana
Alan M
AM
Jones
D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D035264:Flowers / Q000254:growth & development / Q000378:metabolism; D044387:GTP-Binding Protein beta Subunits / Q000378:metabolism; D015870:Gene Expression; D018506:Gene Expression Regulation, Plant; D007210:Indoleacetic Acids / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000502:physiology*; D018519:Meristem / Q000254:growth & development* / Q000378:metabolism; D010641:Phenotype
C089590:AGB1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D044387:GTP-Binding Protein beta Subunits; D007210:Indoleacetic Acids; D047908:Intracellular Signaling Peptides and Proteins; C435920:MAX2 protein, Arabidopsis; C547880:NDL1 protein, Arabidopsis