The YSL proteins are a group of membrane transport proteins that belong to oligopeptide transporters (OPTs). This gene family codes for the integral membrane proteins which are found in fungi, plants, archaebacteria, and in some of the bacterial species. The YSL involves in the process of distributing the chelated metal ions forming a distinct clade that are assumed to have less defined functions. In Arabidopsis thaliana, the defective expression of the AtOPT3 gene makes the accumulation of more amounts of iron in leaves indicate that the gene is constitutively expressed and up-regulated in response to roots. The role of the OPT gene family was shown to regulate the iron loading phloem that controls the iron deficiency responses in the root system. The OTP gene family found in Arabidopsis thaliana (AtOTPs) and Oryza sativa (OsOTPs) shares about 89% of identity. These transport proteins functions as a part of an iron-responsive network that are co-expressed in both plants.
The nutrient ion transporters in plants
Certain ions of transition metals such as copper, iron, zinc, and iron are found to be very important for the growth and development of the plants, but they become very toxic upon loaded in excess amounts.
For growing healthy plants, various transition metals are essential. These are obtained from the soil and then distributed throughout the various parts of the plant body. The concentration of the transition metal ions is precisely regulated and distributed in different subcellular organelles.
The membrane transporters are very essential that play a central part in nutrient transport and are also used as a powerful tool in most genetic and molecule techniques. These methods have addressed several gene families that are found to be involved in the transport of different transition metal ions.
The OPT gene family of Arabidopsis thaliana:
The transport of heavy metals from the root system to the shoot system is very important for maintaining homeostasis in plants. Here the cadmium (Cd) forms a complex with phytochelatins and thiol-rich oligopeptides in Arabidopsis thaliana. The membrane located transporters are essential in loading Cd ions in the xylem. The OPT3 family of the transporter in the plant plays a significant role in the transport of cadmium.
Many OPT gene families were been identified in other plants, yeast but not in animals. These OPT transport proteins are made up of about 12 to 14 transmembrane proteins with two conserved motifs such as 1) NPG and 2) KIPPR. Certain members of OPT families that are found in Arabidopsis thaliana were also found as heterologous systems in Saccharomyces cerevisiae as in the form of synthetic tetrapeptides such as KLGL, and KLLG or as pentapeptides such as KLLLG.
It was found that the OPTs have a major role in maintaining ion homeostasis. For example, the mRNA products of AtOPT2 and AtOPT3 are induced by minerals shortage along with the heterologous expression of AtOPT3 that helps in the restoration of copper, manganese, and iron defects in the mutants of Arabidopsis thaliana. The null mutation of this gene family induces the embryonic lethality that occurs due to the effect of iron movement during the seed developmental stage.
Certain OPTs are also involved in the short oligopeptide transport across the plasma membrane. The OPT3 induces the root to leaf transport of cadmium, phytochelatins, and the reduced glutathione (GSH). More the root sensitivity makes their leaves less sensitive to OPT3 to cadmium compared to their wild strains. Other classes of OPTs are found to be involved in the metal chelates transport that includes AtOPT6 that transport glutathione (reduced) and the cadmium-glutathione complex.
