Barley cysteine protease PAP14 plays a role in degradation of chloroplast proteins

Abstract

HvPAP14 is a cysteine protease found in association with thylakoid membranes. Among its putative substrates are proteins such as LHCB1, LHCB5, PSBO, and RbcL, as revealed in overexpressing barley plants.

Papain-like cysteine proteases are required for the regulation of photosynthetic gene expression and acclimation to high light stress

“…The data presented here implicate chloroplast and cytosolic cysteine proteases in the Rubisco degradation process. These data agree with a recent report concerning the barley HvPAP14 protease, which is involved in the degradation of the large subunit of Rubisco and thylakoid membrane proteins ( Frank et al , 2019 ).…”

“…These findings suggest that OC-I-inhibited protease targets in the chloroplasts are involved in pigment biosynthesis and/or degradation. Possible candidates are the degradation of the pigment–protein complexes ( Buet et al , 2019 ; Frank et al , 2019 ) and the tetrapyrrole biosynthesis pathway ( Eckhardt et al , 2004 ; Tanaka and Tanaka, 2007 ). Both of these pathways can generate signals, such as singlet oxygen that are involved in chloroplast to nucleus signalling ( Rintamäki et al , 2009 ; Leister, 2019 ).…”

“…While plant cysteine proteases fulfil many important functions in plants, they have never been shown to localize to chloroplasts, except in barley ( Frank et al , 2019 ). The major chloroplast protease families (Clp, FtsH, and DegP) are constitutively expressed and fulfil roles in protein quality control and the maintenance of photosynthesis rather than large-scale remodelling of the chloroplast proteome.…”

“…Despite intensive efforts, molecular–genetic and biochemical studies have failed to identify chloroplast-localized cysteine proteases in Arabidopsis and plant species. However, a barley C1A family cysteine protease, called HvPAP14, was recently found in the thylakoid lumen of the chloroplasts, as well as the endoplasmic reticulum and vesicular bodies ( Frank et al , 2019 ). HvPAP14 is involved in the degradation of the light-harvesting Chl a / b -binding proteins and the large subunit of Rubisco ( Frank et al , 2019 ).…”

“…However, a barley C1A family cysteine protease, called HvPAP14, was recently found in the thylakoid lumen of the chloroplasts, as well as the endoplasmic reticulum and vesicular bodies ( Frank et al , 2019 ). HvPAP14 is involved in the degradation of the light-harvesting Chl a / b -binding proteins and the large subunit of Rubisco ( Frank et al , 2019 ). There is only one other report which has provided evidence of cysteine protease activity in the thylakoid lumen ( Sokolenko et al , 1997 ).…”