8.A.234.  The Modifier of Hyperactive ACD6 (MHA1) Family 

The ACD6.1 or MHA1 proteins are small proteins that modulate ion-channel-like ACD6 (TC# 9.A.43.1.14) to regulate immunity in Arabidopsis thaliana. Two loci, MODULATOR OF HYPERACTIVE ACD6.1 (MHA1) and its paralog MHA1-LIKE (MHA1L), that code for approximately 7 kDa proteins, differentially interact with specific ACD6 variants. MHA1L enhances the accumulation of an ACD6 complex, thereby increasing the activity of the ACD6 standard allele for regulating plant growth and defenses. The intracellular ankyrin repeats of ACD6 are structurally similar to those found in mammalian ion channels. Several lines of evidence link increased ACD6 activity to enhanced calcium influx, with MHA1L is a direct regulator of ACD6, indicating that peptide-regulated ion channels are not restricted to animals (Chen et al. 2023).