Protein modification
Modification of cell wall properties has been considered as one of the determinants that confer aluminum (Al) tolerance in plants, while how cell wall modifying processes are regulated remains elusive. Here, we present a WRKY transcription factor WRKY47 involved in Al tolerance and root growth. Lack of WRKY47 significantly reduces, while overexpression of it increases Al tolerance. We show that lack of WRKY47 substantially affects subcellular Al distribution in the root, with Al content decreased in apoplast and increased in symplast, which is attributed to the reduced cell wall Al‐binding capacity conferred by the decreased content of hemicellulose I in the wrky47‐1 mutant. Based on microarray, real time‐quantitative polymerase chain reaction and chromatin immunoprecipitation assays, we further show that WRKY47 directly regulates the expression of EXTENSIN‐LIKE PROTEIN (ELP ) and XYLOGLUCAN ENDOTRANSGLUCOSYLASE‐HYDROLASES17 (XTH17 ) responsible for cell wall modification. Increasing the expression of ELP and XTH17 rescued Al tolerance as well as root growth in wrky47‐1 mutant. In summary, our results demonstrate that WRKY47 is required for root growth under both normal and Al stress conditions via direct regulation of cell wall modification genes, and that the balance of Al distribution between root apoplast and symplast conferred by WRKY47 is important for Al tolerance.
The amino‐terminal residue of a protein (or amino‐terminus of a peptide following protease cleavage) can be an important determinant of its stability, through the Ubiquitin Proteasome System associated N‐degron pathways. Plants contain a unique combination of N‐degron pathways (previously called the N‐end rule pathways) E3 ligases, PROTEOLYSIS (PRT)6 and PRT1, recognizing non‐overlapping sets of amino‐terminal residues, and others remain to be identified. Although only very few substrates of PRT1 or PRT6 have been identified, substrates of the oxygen and nitric oxide sensing branch of the PRT6 N‐degron pathway include key nuclear‐located transcription factors (ETHYLENE RESPONSE FACTOR VIIs and LITTLE ZIPPER 2) and the histone‐modifying Polycomb Repressive Complex 2 component VERNALIZATION 2. In response to reduced oxygen or nitric oxide levels (and other mechanisms that reduce pathway activity) these stabilized substrates regulate diverse aspects of growth and development, including response to flooding, salinity, vernalization (cold‐induced flowering) and shoot apical meristem function. The N‐degron pathways show great promise for use in the improvement of crop performance and for biotechnological applications. Upstream proteases, components of the different pathways and associated substrates still remain to be identified and characterized to fully appreciate how regulation of protein stability through the amino‐terminal residue impacts plant biology.