Multi-level analysis of the interactions between REVOLUTA and MORE AXILLARY BRANCHES 2 in controlling plant development reveals parallel, independent and antagonistic functions

Class III homeodomain leucine zipper (HD-ZIPIII) transcription factors play fundamental roles in controlling plant development. The known HD-ZIPIII target genes encode proteins involved in the production and dissipation of the auxin signal, HD-ZIPII transcription factors and components that feedback to regulate HD-ZIPIII expression or protein activity. Here, we have investigated the regulatory hierarchies of the control of MORE AXILLARY BRANCHES2 (MAX2) by the HD-ZIPIII protein REVOLUTA (REV). We found that REV can interact with the promoter of MAX2. In agreement, rev10D gain-of-function mutants had increased levels of MAX2 expression, while rev loss-of-function mutants showed lower levels of MAX2 in some tissues. Like REV, MAX2 plays known roles in the control of plant architecture, photobiology and senescence, which prompted us to initiate a multi-level analysis of growth phenotypes of hd-zipIII, max2 and respective higher order mutants thereof. Our data suggest a complex relationship of synergistic and antagonistic activities between REV and MAX2; these interactions appear to depend on the developmental context and do not all involve the direct regulation of MAX2 by REV.