A New Role for SAG12 Cysteine Protease in Roots of Arabidopsis thaliana

Abstract

Senescence associated gene (SAG) 12, which encodes a cysteine protease is considered to be important in nitrogen (N) allocation to Arabidopsis thaliana seeds. A decrease in the yield and N content of the seeds was observed in the Arabidopsis SAG12 knockout mutants (sag12) relative to the wild type (Col0) under limited nitrogen nutrition. However, leaf senescence was similar in both lines. To test whether SAG12 is involved in N remobilization from organs other than the leaves, we tested whether root N could be used in N mobilization to the seeds. Root architecture, N uptake capacity and 15N partitioning were compared in the wild type and sag12 under either high nitrogen (HN) or low nitrogen (LN) conditions. No differences in root architecture or root N uptake capacity were observed between the lines under HN or LN. However, under LN conditions, there was an accumulation of 15N in the sag12 roots compared to the wild type with lower allocation of 15N to the seeds. This was accompanied by an increase in root N protein contents and a significant decrease in root cysteine protease activity. SAG12 is expressed in the root stele of the plants at the reproductive stage, particularly under conditions of LN nutrition. Taken together, these results suggest a new role for SAG12. This cysteine protease plays a crucial role in root N remobilization that ensures seed filling and sustains yields when nitrogen availability is low.

H2O2 as a Feedback Signal on Dual-Located WHIRLY1 Associates with Leaf Senescence in Arabidopsis

“…The nWHY1 plant, which accumulated approximately 4-fold higher WHY1 transcripts over WT plants, had apparently lower expression levels for its repressed targets WRKY53 and WRKY33, as well as SEN4. But on the other hand, this line expressed significantly higher SAG12 and SAG29 (Figure 2), which encoded, respectively, a cysteine protease and a sucrose transporter and functioned in remobilization of nitrogen and carbon in senescent organs as well as in normal organs under stress conditions [45][46][47]. This line showed more or less delayed leaf senescence as compared to the why1 mutant or WT (Figure 1).…”

Autophagy and Nutrients Management in Plants

“…Although both autophagy and cysteine proteases are key players during leaf senescence, protein proteolysis, and nutrient recycling, as shown by recent publications from James et al [86,87], the relationship between them remains largely unknown. It is admitted that proteins are not degraded inside the autophagosomes but rather transported by them to the lytic vacuoles where proteases and hydrolases operate.…”

Plant Proteases: From Key Enzymes in Germination to Allies for Fighting Human Gluten-Related Disorders

“…Plant proteases have been described to accomplish multiple roles in different physiological processes along the plant life cycle, such as programmed cell death, senescence, abscission, fruit ripening, plant growth, and N homeostasis (Grudkowska and Zagdańska, 2004; van der Hoorn, 2008; Liu et al, 2018; Tornkvist et al, 2019). In response to abiotic and biotic stresses, proteases are also involved in nutrient remobilization associated with leaf and root proteins degradation to ensure yield (Diaz-Mendoza et al, 2014; Velasco-Arroyo et al, 2016, 2018; Gomez-Sanchez et al, 2019; James et al, 2019), or in triggering the response of the plant to pathogens and phytophagous insects and acari (van der Hoorn and Jones, 2004; Shindo and van der Hoorn, 2008; Misas-Villamil et al, 2016; Diaz-Mendoza et al, 2017). Moreover, plant proteases play a crucial role in the plant seed germination, through the mobilization of other proteins accumulated in seeds and cereal grains (Grudkowska and Zagdańska, 2004; Cambra et al, 2012; Diaz-Mendoza et al, 2016; Szewinska et al, 2016; Liu et al, 2018; Radchuk et al, 2018).…”