Symposium IV: Evolution of Plant Development

Abs # 40003: The Development and Evolution of Compound Leaves

Presenter:	Sinha, Neelima R, nrsinha@ucdavis.edu
Authors	Sinha, Neelima R (A)   Kim, Minsung  (A)   Chung, Kook-Hyun  (A)   Goliber, Tom  (A)   Bharathan, Geeta  (B)   Kessler, Sharon  (A)   Gerttula, Suzanne  (A)   Champagne, Connie  (A)
Affiliations:	(A): Section Of Plant Biology, University of California, Davis, CA - 95616 (B): Department of Ecology and Evolution, SUNY, Stony Brook, NY - 11794-5245

The Class I Knotted-like homeobox (KNOX 1) genes are highly expressed in the shoot apical meristem but not expressed in the emerging leaf primordium in maize or Arabidopsis. In tomato, KNOX1 expression (LeT6, TKN1) is seen in the early leaf primordium (Chen et al. 1997; Hareven et al. 1996). We have shown that this early expression of KNOX 1 genes in the tomato leaf primordium causes it to take on a compound fate in tomato (Sinha 1997). In order to thoroughly test this hypothesis we have completed an analyses at several different phylogenetic levels. We have mapped the trait of compound leaves on the green plant evolutionary tree to identify genera in which compound leaves arose independently. This tree includes cycads and multiple independent origins in the dicot families. We have analyzed compound leaf producing shoot apices in all these clades except the monocots and found that in all instances except one (a derived clade in the Fabaceae) compound leaves always show expression of KNOX genes (Bharathan et al., 2002). In the derived pea clade the LFY/FLO gene regulates this function of generating leaf complexity. While KNOX genes appear to be important for generating leaf complexity (except in a derived clade in the Fabaceae) we find that other genes like PHANTASTICA might play a role in determining the form of the compound leaf generated. Transgenic plants overexpressing antisense PHAN suggest that PHAN, by modulating dorsiventrality, has a role in regulating the number of leaflets and their placement in a compound leaf. In Neobeckia aquatica, leaves with different morphologies are produced depending on environmental conditions. Simple leaves are produced under high-light terrestrial conditions while lobed and compound or highly dissected leaves are produced under low-light terrestrial and underwater conditions, respectively. Experiments in our lab show that GA can induce the production of simple leaves on plants exposed to conditions that normally induce compound leaves (and Unaconalzole can lead to an opposite effect). The expression differences between these two phenotypic states are being explored. With these experiments we hope to understand a basic problem in plant biology - why some derivatives from the shoot apical meristem are simple, while others can be compound, and how these alternate morphologies may have arisen in evolutionary time.