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

Abstract

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 <i>HD-ZIPIII</i> expression or protein activity. Here, we have investigated the regulatory hierarchies of the control of <i>MORE AXILLARY BRANCHES2</i> (<i>MAX2</i>) by the HD-ZIPIII protein REVOLUTA (REV). We found that REV can interact with the promoter of <i>MAX2</i> In agreement, <i>rev10D</i> gain-of-function mutants had increased levels of <i>MAX2</i> expression, while <i>rev</i> loss-of-function mutants showed lower levels of <i>MAX2</i> 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 <i>hd-zipIII</i>, <i>max2</i> 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 <i>MAX2</i> by REV.