Youssef Bouargalne

Thesis started november 1st, 2018 - Defended june 10^th 2022
Funding: Région Bretagne - Université Rennes 1
Direction: C. Deleu, F. Le Caherec

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Abstract:

Class II WSCP (WSCPII) are non-photosynthetic soluble proteins that bind chlorophyll, and have been found so far only in Brassicaceae. These proteins belong to the Kunitz-type protease inhibitor (PI) family and some of them are overexpressed under abiotic stress conditions. Little is known about the dual function of WSCPII and their physiological role is much more limited. The aim of this study was to characterize the function of WSCPII from rapeseed. We first showed that BnD22, the major rapeseed leaf WSCPII, is a bifunctional protein that inhibit Cys proteases and bind Chls with preferential affinity to Chla. These two functions can be simultaneous with an enhanced inhibitory activity when proteins are complexed with Chls. Moreover, we demonstrated that BnD22 is not localized in the chloroplast but in the endoplasmic reticulum and the vacuole. Furthermore, we have demonstrated that rapeseed possesses a multigene family of WSCPII, split into distinct groups associated to preferential binding to Chla or Chlb or the loss of Chl-binding capacity. Rapeseed WSCPII exhibit organ- and developmental
stage- specific expression patterns and they possess diverse or redundant functional properties. Altogether, these results allow to understand the functional properties of WSCPII that may open new gate to understand their physiological roles.