Environmental regulation of lateral root emergence in Medicago truncatula requires the HD-Zip I transcription factor HB1

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

La Plata

Congreso; Reunión Argentina de Fisiología Vegetal; 2010

Sociedad Argentina de Fisiología Vegetal

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 HB1 is expressed in primary and lateral root meristems and induced by salt stress. Constitutive expression of HB1 in M. truncatula roots alters their architecture, whereas hb1 TILLING mutants showed increased lateral root emergence. EMSA, promoter mutagenesis and ChIP-PCR assays revealed that HB1 directly recognizes a CAATAATTG cis-element present in the promoter of a LOB-like (Lateral Organ Boundaries) gene, LBD1, transcriptionally regulated by auxin. Expression of these genes in response to ABA and auxin and their behavior in hb1 mutants revealed an HB1-mediated repression of LBD1 acting during LR emergence. M. truncatula HB1 regulates an adaptive developmental response to minimize the root surface exposed to adverse environmental stresses.