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Unformatted text preview: JPR SYMPOSIUM Weeds of change: Cardamine hirsuta as a new model system for studying dissected leaf development Claudia Canales • Michalis Barkoulas • Carla Galinha • Miltos Tsiantis Received: 28 May 2009 / Accepted: 24 August 2009 / Published online: 8 October 2009 Ó The Botanical Society of Japan and Springer 2009 Abstract Cardamine hirsuta , a small crucifer closely related to the model organism Arabidopsis thaliana , offers high genetic tractability and has emerged as a powerful system for studying the genetic basis for diversification of plant form. Contrary to A. thaliana , which has simple leaves, C. hirsuta produces dissected leaves divided into individual units called leaflets. Leaflet formation requires activity of Class I KNOTTED1-like homeodomain (KNOX) proteins, which also promote function of the shoot apical meristem (SAM). In C. hirsuta , KNOX genes are expressed in the leaves whereas in A. thaliana their expression is confined to the SAM, and differences in expression arise through cis-regulatory divergence of KNOX regulation. KNOX activity in C. hirsuta leaves delays the transition from proliferative growth to differ- entiation thus facilitating the generation of lateral growth axes that give rise to leaflets. These axes reflect the sequential generation of cell division foci across the leaf proximodistal axis in response to auxin activity maxima, which are generated by the PINFORMED1 (PIN1) auxin efflux carriers in a process that resembles organogenesis at the SAM. Delimitation of C. hirsuta leaflets also requires the activity of CUP SHAPED COTYLEDON ( CUC ) genes, which direct formation of organ boundaries at the SAM. These observations show how species-specific deployment of fundamental shoot development networks may have sculpted simple versus dissected leaf forms. These studies also illustrate how extending developmental genetic studies to morphologically divergent relatives of model organisms can greatly help elucidate the mechanisms underlying the evolution of form. Keywords Leaf development Auxin KNOX proteins Introduction A key challenge in biology is to understand how the extraordinary diversity in morphology is generated. Leaves of seed plants show remarkable differences in form and thus provide an excellent system to study morphological evolution. Although all leaf primordia develop initially as simple structures, morphology diverges during develop- ment so that mature leaves of different species vary greatly in form (Bharathan et al. 2002 ; Dengler and Tsukaya 2001 ). Leaves can be classified as simple, in which the leaf blade is entire, or dissected, in which the leaf blade is subdivided into individual units termed leaflets. The mar- gins of simple leaves and leaflets can also present varying degrees of complexity, bearing serrations and lobes....
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This note was uploaded on 10/31/2010 for the course CBNS 108 taught by Professor Green,demason during the Spring '10 term at UC Riverside.
- Spring '10
- The Land