found that KNOX1 protein expression in Cercis occurs both in the SAM and in developing mature leaves. Species in these genera lack complex compound leaves, though they may be bilobed, leading to a question of whether they are truly simple leaves or are simplified from compound-leaved ancestors. (2000), based on plastid matK gene sequences, Cercis (redbud) and Bauhinia were found to be sisters to the rest of Fabaceae. This suggests that soon after the IRLC diverged from its closest living relatives there was a loss of KNOX1 expression during compound leaf development.įrom a phylogenetic analysis by Wojciechowski et al. However, a noticeable difference in KNOX1 expression was evident in the later development of compound leaves: developing compound leaves of IRLC members (pea, wisteria, alfalfa, and fava bean) all failed to show KNOX1 expression, whereas compound-leaved Fabaceae outside the IRLC (including soybean, bean, Mimosa, Lotus, and Acacia) all showed KNOX1 expression in developing leaves. first make use of a polyclonal KNOX1-specific antibody to show that KNOX1 expression is downregulated in incipient leaf primordia both in IRLC members, such as alfalfa and Chinese wisteria, and IRLC nonmembers such as soybean ( Glycine) and bean ( Phaseolus).

The authors hypothesize that overlapping functionality of KNOX1 and FLO/LFY genes in ancestral Fabaceae species enabled the loss of KNOX1 function in compound leaf development in the IRLC.Ĭhampagne et al. Results of further experiments suggest that orthologs of FLORICAULA/LEAFY ( FLO/LFY) function in place of KNOX1 genes in the development of compound leaves in the IRLC. ), except for a large subclade known as the inverted repeat–lacking clade (IRLC), which includes fava bean ( Vicia), pea ( Pisum), and alfalfa ( Medicago). (E) to (H) Non-IRLC members Cercis (E), soybean (F), Acacia (G), and bean ( Phaseolus ). (A) to (D) IRLC members pea (A), wisteria (B), alfalfa (C), and fava bean (D). These observations suggest that compound leaves generally evolve from simple leaves by the induction of KNOX1 genes in the developing leaf, causing leaves to become somewhat shoot like. Furthermore, overexpression of a KNOX1 homolog in tomato leads to more highly branched compound leaf forms. By contrast, many compound-leaved species show a reactivation of KNOX1 expression during leaf development.

In some cases, ectopic expression in simple leaves results in altered leaf morphology reminiscent of compound leaves (ectopic outgrowths and lobes, and in some cases, ectopic meristems). Their expression is repressed in leaf primordia and throughout leaf development, consistent with the determinate growth of these organs. In simple-leaved plants, such as maize or Arabidopsis, class I KNOX1 genes are expressed in the shoot apical meristem, where they function to maintain indeterminacy. Class I KNOTTED-like ( KNOX1) genes have been found to play an important role in the development of compound leaves in many vascular plants ( Bharathan et al., 2002). Plant leaves exist in a dizzying array of shapes and sizes, from the tiny duckweed ( Lemna minor) to the enormous Raphia palm ( Raphia farinifera), and the simple-leaved poplar ( Populus sp) to the deeply lobed oak ( Quercus spp) or the delicate compound-leaved Mimosa spp.

Primordia plant