Figure 12.

MtCAS31 (described in Figure 10) is: (a) upregulated upon dehydration and the protein it encodes; (b) binds the plasmamembrane intrinsic protein aquaporin MtPIP2;7 (Medtr2g094270) as well as the Medicago AUTOPHAGY-RELATED GENE8 Protein (ATG8a; Medtr4g037225) through the 2 AIM-like motifs (Autophagy Interacting Motifs) located near the MtCAS31 amino terminus. Thus, MtCAS31 acts as an adaptor protein; (c) directly linking its cargo protein MtPIP2;7 with ATG8a in phagophores, which leads to the destruction of the aquaporins (and MtCAS31) through selective autophagy. While stress is present, so too is MtCAS31, which ensures a continuous turnover of MtPIP2;7. The molecular consequences are a reduction in the number of aquaporins located in the plasma membrane of drought-stressed Medicago cells. The phenotypic consequences for the cell when MtCAS31 is present are: (d) an altered hydraulic conductivity of the cell membrane, resulting in a physiology tuned to reduce water transport across the cell membrane.