Ricerc@Sapienza

The plant cell wall (CW) is a complex extracellular matrix mostly composed of polysaccharides, phenolics and glycoproteins. The CW surrounds every plant cell and provides mechanical support, countering turgor pressure and determining cell extensibility and thus controlling cell shape and size. Once germinated, seedlings form a protective structure, the apical hook, to prevent damage to the apical meristem. The formation of a proper hook requires hypocotyl bending via differential epidermal cell elongation among the inner and external sides of the hook. The phytohormone auxin orchestrates differential growth through its asymmetric accumulation at the concave side, with auxin maxima correlating with the inhibition of cell elongation. A tight interaction between CW and hormonal pathways mediates the differential cell elongation in hook formation. Xyloglucan deficiency in the CW compromises auxin distribution, impairing auxin maxima formation and disrupting hook development. Mutations or chemical treatments altering CW composition determine the activation of compensatory mechanisms aimed to reestablishing the correct CW functionality, such as CW stiffening and accumulation of jasmonic acid (JA) and salicylic acid (SA), which are known to antagonize apical hook formation. In this project I will investigate the actors downstream of CW alterations which impair proper apical hook development. In particular, throughout phenotypic analysis of CW mutants, quantification of the physiological response, localization and quantification of ROS levels I expect to gain new insight over the role of different CW components, of CW integrity maintenance responses and of ROS homeostasis in hook formation and, more generally, in differential cell expansion.