An HD-Zip I transcription factor in the environmental control of legume root developmental plasticity

ARIEL FD; DIET A; VERDENAUD M; GRUBER V; FRUGIER F; CHAN RL; CRESPI M

PLANT CELL

AMER SOC PLANT BIOLOGISTS

Año: 2010 vol. 22 p. 2171 - 2183

1040-4651

The adaptation of root architecture to environmental constraints is a major agricultural trait, notably in legumes, the third main crop worldwide. This root developmental plasticity depends on the formation of lateral roots (LRs) emerging from primary roots. In the model legume Medicago truncatula, the HD-Zip I transcription factor (TF) Mt HB1 is expressed in primary and lateral root meristems and induced by salt stress. Constitutive expression of Mt HB1 in M. truncatula roots alters their architecture, whereas Mt HB1 TILLING mutants showed increased lateral root emergence. EMSA, promoter mutagenesis and ChIP-PCR assays revealed that Mt HB1 directly recognizes a CAATAATTG cis-element present in the promoter of a LOB-like (Lateral Organ Boundaries) gene, Mt LBD1, transcriptionally regulated by auxin. Expression of these genes in response to ABA and auxin and their behavior in hb1 mutants revealed an Mt HB1-mediated repression of Mt LBD1 acting during LR emergence. Mt HB1 controls an adaptive developmental response to minimize the root surface exposed to adverse environmental stresses.