A Brassica napus water soluble chlorophyll binding protein (WSCP1) delays chlorophyll degradation and inhibits serine proteases during dark-induced leaf senescence in Arabidopsis thaliana.

Main conclusion: This preliminary study shows that Brassica napus WSCP1 delays chlorophyll degradation and inhibits serine proteases during dark-induced leaf senescence in Arabidopsis. In Brassica napus L., one of the levers for improving Nitrogen Remobilization Efficiency (NRE) consists to delay senescence onset, which prolongs leaf lifespan and reduces the asynchronism between the nitrogen emptying period in these source organs and the filling period of seeds. Water soluble chlorophyll binding proteins (WSCPs) may have a dual function in chlorophyll protection and protease inhibition. As such they are excellent candidates to propose a technical solution to delay leaf senescence. Several isoforms of WSCPs have been identified in the leaves of rapeseed. Among them, WSCP1 presents two motifs in its protein sequence that are associated to the putative dual function. To test if WSCP1 can actually delay leaf senescence, the overexpression of WSCP1 under the control of the SAG12 senescence promoter (pSAG12::WSCP1) was developed in an Arabidopsis thaliana accession that was previously described as early senescent (RIL232). During dark-induced senescence, our main results reveal a lower chlorophyll degradation and a reduction of the serine proteases (SPs) activity in leaves of pSAG12::WSCP1 lines compared to RIL232. Although SP inhibition was strong in pSAG12::WSCP1 leaves compared with RIL232, no difference in leaf protein content was observed. This result suggests either the recruitment of a compensatory proteolytic system in WSCP1-overexpressing lines or that SPs are not essential for protein nitrogen remobilization during dark-induced leaf senescence.