PARAQUAT RESISTANT1, a Golgi-Localized Putative Transporter Protein, Is Involved in Intracellular Transport of Paraquat    

Abstract

Paraquat is one of the most widely used herbicides worldwide. In green plants, paraquat targets the chloroplast by transferring electrons from photosystem I to molecular oxygen to generate toxic reactive oxygen species, which efficiently induce membrane damage and cell death. A number of paraquat-resistant biotypes of weeds and Arabidopsis (Arabidopsis thaliana) mutants have been identified. The herbicide resistance in Arabidopsis is partly attributed to a reduced uptake of paraquat through plasma membrane-localized transporters. However, the biochemical mechanism of paraquat resistance remains poorly understood. Here, we report the identification and characterization of an Arabidopsis paraquat resistant1 (par1) mutant that shows strong resistance to the herbicide without detectable developmental abnormalities. PAR1 encodes a putative L-type amino acid transporter protein localized to the Golgi apparatus. Compared with the wild-type plants, the par1 mutant plants show similar efficiency of paraquat uptake, suggesting that PAR1 is not directly responsible for the intercellular uptake of paraquat. However, the par1 mutation caused a reduction in the accumulation of paraquat in the chloroplast, suggesting that PAR1 is involved in the intracellular transport of paraquat into the chloroplast. We identified a PAR1-like gene, OsPAR1, in rice (Oryza sativa). Whereas the overexpression of OsPAR1 resulted in hypersensitivity to paraquat, the knockdown of its expression using RNA interference conferred paraquat resistance on the transgenic rice plants. These findings reveal a unique mechanism by which paraquat is actively transported into the chloroplast and also provide a practical approach for genetic manipulations of paraquat resistance in crops.

Polyamine Transport Systems in Plants

“…The par1 mutants are resistant to PQ and have lower levels of PQ accumulation in chloroplasts, suggesting that PAR1 is involved in the intracellular transport of PQ into chloroplasts. The same research group also identifi ed the rice gene OsPAR1 (identical to OsPUT2 ), which regulates rice sensitivity to PQ similarly to that of PAR1 in Arabidopsis (Li et al 2013 ). Collectively, Arabidopsis and rice LAT/PUT genes are involved in PA/PQ transport.…”

“…RMV1-GFP fusion protein localizes to the plasma membrane when transiently expressed in onion epidermal cells or when constitutively expressed in transgenic Arabidopsis . By contrast, transient expression analysis using Arabidopsis protoplasts indicate that PAR1/AtLAT4/AtPUT2 localizes to the Golgi apparatus, and AtPUT1/AtLAT3 localizes to the endoplasmic reticulum (Li et al 2013 ). Rice OsPAR1/OsPUT2 also localizes to the Golgi apparatus (Li et al 2013 ).…”

“…However, a hidden Markov model based on multiple alignments indicated that plant PUT genes were not homologous with animal LAT genes (Mulangi et al 2012a ), suggesting that they have different functions resulting from low sequence homology. The AtPUT2/AtLAT4 gene was recently identifi ed as the gene responsible for the paraquat resistant 1 ( par1 ) mutation (Li et al 2013 ). The par1 mutants are resistant to PQ and have lower levels of PQ accumulation in chloroplasts, suggesting that PAR1 is involved in the intracellular transport of PQ into chloroplasts.…”

Long-Distance Transport of Thiamine (Vitamin B1) Is Concomitant with That of Polyamines

“…As noted previously, PUT3 has four additional homologs in Arabidopsis, which although not found in our yeast screen may add a level of redundancy to this transporter family and should be assessed for their contribution to the transport of vitamin B 1 in planta. Interestingly, the Arabidopsis PUT family appears to have a divergent pattern of tissue expression as assessed by reverse transcription PCR (Mulangi et al, 2012), as well as divergent intracellular localization patterns (Li et al, 2013), which may suggest specialization in a spatial manner. Notwithstanding, the small deficit of B 1 vitamers observed in rmv1 may contribute to the stunted root phenotype but is likely to have a stronger contribution from the disruption in polyamine homeostasis (see below).…”

“…Although polyamine metabolism has been studied extensively, little is known of its transport in plants with the exception of the recently identified PUT family (Fujita et al, 2012;Mulangi et al, 2012) and the OCT1 transporter from Arabidopsis (Arabidopsis thaliana) that is implicated in Cad transport (Strohm et al, 2015). The PUT family of proteins is localized at the cellular level to various compartments, including the plasma membrane, Golgi apparatus, and endoplasmic reticulum (Fujita et al, 2012;Li et al, 2013). However, polyamine homeostasis is also regulated by long-distance transport, and indeed their presence in the vascular system of plants has been established in several species (Friedman et al, 1986;Pommerrenig et al, 2011;Sood and Nagar, 2005;Yokota et al, 1994).…”