Prof.  Iqbal  Hussain
Government College University, Faisalabad,  Pakistan

Title: Functions and transport of silicon in plants

Abstract:

Silicon exerts beneficial effects on plant growth and production by alleviating both biotic and abiotic stresses including diseases, pests, lodging, drought, and nutrient imbalance. Recently, two genes (Lsi1 and Lsi2) encoding Si transporters have been identified. Since the first Si transporter, Lsi1 was identified in rice in 2006, a number of Si transporters have been identified in different plant species. Lsi1 (low silicon 1) belongs to a Nod 26-like major intrinsic protein subfamily in aquaporin. Lsi1 is localized on the distal side of both exodermis and endodermis in rice roots. Homologs of rice Lsi1 has been isolated and functionally characterized in barley, maize, wheat, pumpkin and horsetail. Lsi1 shows influx transport activity for Si, therefore, Lsi1 is responsible for transport of Si from the external solution to the root cells. On the other hand, Lsi2 encodes a putative anion transporter have also been identified in rice, barley, maize and pumpkin. Lsi2 is localized on the proximal side of the same cells. Lsi2 is an efflux transporter responsible for the transport of Si from the root cells to the apoplast. Different plant species show distinct expression pattern and cellular localization of Lsi1 and Lsi2. After Si uptake by the roots, the translocation of Si from the roots to the shoots is mediated by Lsi3, a homolog of Lsi2 in rice. It is localized to the root pericyclic cells. On the other hand, a homolog of Lsi1, Lsi6 mediates xylem unloading of Si. Knockout of this gene resulted in disturbed Si deposition pattern in the leaves. Final distribution of Si to the grain (mainly husk) is mediated by three different transporters, Lsi2, Lsi3 and Lsi6 in rice. All of them show high expression in the nodes, a place for mineral distribution. Lsi6 is localized at the xylem transfer cells of enlarged vascular bundle, whereas Lsi2 is localized at distal side of a parenchyma cell layer surrounding the enlarged vascular bundles, which is the next cell layer of xylem transfer cells and Lsi3 is localized at the parenchyma tissues between enlarged- and diffuse vascular bundles. Knockout of Lsi6, Lsi2 or Lsi3 resulted in decreased Si accumulation on the husk, but increased Si accumulation in the flag leaf, indicating that cooperation of these transporters localized at the different cell layers are required for inter-vascular transfer of Si from enlarged vascular bundles to diffuse vascular bundles for preferential distribution of Si in the husk. Similar system on such inter-vascular transfer of Si in barley was also observed. In my talk, I will introduce recent progress made in Si transporter researches.

Keywords: Silicon, stress, beneficial effect, transporter, accumulation.
• Sumaira Thind, Iqbal Hussain, Shafaqat Ali, Rizwan Rasheed and Muhammad Arslan Ashraf (2021). Silicon application modulates growth, physio-chemicals and antioxidants in wheat (Triticum aestivum L.) exposed to different cadmium regimes. Dose-Response, 19 (2):1-15.
• Sumaira Thind, Iqbal Hussain, Shafaqat Ali, Saddam Hussain, Rizwan Rasheed, Basharat Ali, Hafiz Athar Hussain (2020). Physiological and biochemical bases of foliar silicon-induced alleviation of cadmium toxicity in wheat. Journal of Soil Science and Plant Nutrition, 20(4), 2714-2730.
• Iqbal Hussain, Abida Parveen, Rizwan Rasheed, Muhammad Arslan Ashraf, Muhammad Ibrahim, Saima Riaz, Zarbhakhat Afzaal, and Muhammad Iqbal (2019). Exogenous silicon modulates growth, physio-chemicals and antioxidants in barley (Hordeum vulgare L.) exposed to different temperature regimes. Silicon, 11, 2753–2762.
• Iqbal Hussain, Muhammad Arslan Ashraf, Rizwan Rasheed, Anum Asghar, Muhammad Asim Sajid, Muhammad Iqbal. (2015). Exogenous application of silicon at the boot stage decreases accumulation of cadmium in wheat grains. Brazilian Journal of Botany, 38(2), 223-234.

Biography:

Research Interest:    Plant Stress Physiology, Plant Molecular Biology, Identification of Physio-biochemical Markers of stress tolerance, Thermal adaptation of plants for studying molecular and genetic mechanisms, QTLs study and Photochemistry

  Education:

PhD (2004-2009): Botany (Plant Stress Physiology and Molecular Biology), University of Agriculture, Faisalabad (a part of thesis research was completed under International Research Support Initiative Program (IRSIP) of HEC, Pakistan, under the supervision of Dr. Tadashi Sato, Department of Environmental Life Sciences, Graduate School of Life Sciences, Tohoku University, Sendai, Japan.

Dissertation: “Seasonal variations in some physiological and molecular responses of   maize (Zea   mays   L.)  under glass house conditions”. Supervisor:  Prof. Dr.  Abdul Wahid, Dept. of Botany, University of Agriculture Faisalabad.

Post-Doc (2016-2017): Foreign Fellowship Program of PHEC awarded for one year from Punjab Higher Education Commission (PHEC), under the supervision of Prof. Dr. Atsushi Higashitani Tadashi (Dean), Department of Environmental Life Sciences, Graduate School of Life Sciences, Tohoku University, Sendai, Japan.