Influence of Suspensor Development on Embryogenesis and its Cell Fate Specification in Arabidopsis thaliana

Abstract

In plants, suspensor is an extra-embryonic structure that protrudes developing embryo into the seed cavity and they were ascertained with various functions including nutrient and hormone transport. However, the development of suspensor and its role in embryogenesis is not well understood. In a forward genetic screen for paternal effect mutants, we identified nma-1 mutant which shows defects in suspensor cell elongation. The mutation in nma-1 was mapped to a locus (At2g33160) which encodes for a putative exo-polygalacturonase. In consequence to the short suspensor phenotype, nma mutant embryos develop slower when compared to WT, suggesting suspensor length is one of the determinants for the developmental progression of the embryo. This result was also verified in another mutant with a short suspensor phenotype, short suspensor (ssp). In addition we show that the NMA function in suspensor cell elongation is cell autonomous. As it was isolated from a paternal effect screen, and we were further able to show that the contribution of paternal allele of NMA towards suspensor cell elongation is stronger than the maternal allele suggesting the unequal parental contributions. These findings demonstrate the role of NMA in suspensor cell elongation and its effect on Arabidopsis embryogenesis. This study provides evidence describing the structural function of suspensor, in addition to its known functions. Besides the role of suspensor in embryogenesis, we also report a study to identify the components of the molecular mechanism which specifies the suspensor cell fate. In Arabidopsis thaliana, suspensor cell fate is determined by a pathway mediated by YODA (YDA), a mitogen activated protein kinase kinase kinase, and SSP is assumed to be involved in YDA activation upon fertilization. In addition, YDA was also shown to function in stomata development. However little is known about the components of the YDA pathway involved in embryogenesis. Therefore, we performed a phospho-mutant screen and split ubiquitin based yeast three hybrid screen to identify components of this pathway. Additionally, we tested known proteins in this pathway which were previously shown to function in stomata development and other selected proteins for protein-protein interaction with YDA. Novel potential candidates isolated will broaden our knowledge about cell fate determination of suspensor and early embryo development.