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The roles of BEL1-like proteins in organ morphogenesis in Arabidopsis thaliana Kumar, Ravi

Abstract

Plant organs originate in distinct temporal and spatial arrangements as primordial outgrowths from meristematic regions. The study of how this process is regulated is of great significance to both developmental biologists and plant breeders. Several genes encoding proteins that regulate meristem function and the subsequent layout of shoot and root architecture have been identified by mutation. For example, STM and BP are members of the KNOX class of regulatory proteins and are involved in meristem function (STM) and inflorescence architecture (BP). In Arabidopsis, the BEL1-like TALE homeodomain (BLH) protein family consists of 13 members that form heterodimeric complexes with KNOX homeodomain proteins including STM and BP. Loss of function of BEL1 results in malformed ovules and female sterility but other organs do not seem to be affected. Northern blots and in-situ hybridization experiments have shown that BEL1 is expressed in the stem, sepals, embryo and the shoot/inflorescence apical meristem. The BEL1 expression outside the ovules is an indication that it might also have functions outside the ovule. The lack of bel1 mutant phenotypes in regions other than the ovule is probably due to functional overlaps with other BLH proteins, since many of these proteins overlap in expression with BEL1 and also have similar interacting partners. During my PhD research I have functionally characterized two additional BLH genes, SAWTOOTH1 (SAW1) and SAWTOOTH2 (SAW2) and tested their relationship to BEL1. I was able to determine that the loss of SAW function causes increased growth in the leaf margins whereas over-expression of SAW1 in the plants caused decreased growth due to both reduced cell expansion as well as cell division. Molecular and genetic analyses revealed that the SAW proteins function in part by repressing BP (and perhaps other Class I KNOX genes) expression in the leaves.

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