HYR is a master regulator of multiple BPs, directly acting as an activator/repressor of TFs and other genes in a network involved in PCM and stressprotective pathways.
- HYR is a master regulator, directly activating photosynthesis genes, cascades of transcription factors and other downstream genes involved in PCM and yield stability under drought and high-temperature environmental stress conditions(Fig. 1).
- Maintenance of the HYR chloroplast membrane structure contributes to the sustained photosynthetic capacity under drought. HYR plays a significant role in conferring drought tolerance and improving GY under drought in rice.
- Functional analysis of the HYR protein activity as a TF show that HYR is primarily involved in direct transcriptional activation of multiple photosynthesis-related processes (Fig. 1), HYR is also involved in a regulatory cascade activating the auxinresponsive TF ARF1 involved in vegetative growth and seed development in rice, capable of binding to the DRO1 drought avoidance gene promoter. HYR was shown to repress OsWRKY72, which is the orthologue of Arabidopsis AtWRKY75 that induces root growth when repressed, supporting the HYR-enhanced root growth phenotype. This was experimentally verified by expressing HYR and OsWRKY72 in rice protoplasts, HYR expression causing WRKY72 repression and EXP8 induction, and WRKY72 overexpression causing EXP8 repression.
- The morpho-physiological programme regulated by HYR expression conditioning superior photosynthetic capacity under elevated CO2, light and temperature offers the potential use of HYR expressing plants to maintain crop growth and yield under environmental stresses associated with climate change.
- The HYR (HIGHER YIELD RICE) gene-expressing transgenic plants here are referred to as HYR lines, as they showed higher GY under well-watered and drought-stress conditions.
In addition the HYR lines expressed multiple component traits involved in photosynthesis, sugar levels, root and shoot biomass and WUE under well-watered and drought-stress conditions.
- HYR lines had brilliant dark-green leaves compared with the WT, with ~15%increased chlorophyll levels and chloroplast number.
- Rice HYR lines are drought tolerant.
- HYR lines also displayed higher accumulation of starch granules in flag-leaf parenchyma, signifying a carbohydrate reserve proximal to the panicle during grain development. In response to increased CO2 concentration and irradiance levels HYR lines revealed increased photosynthetic capacity, as well as higher CO2 and light saturation points than WT.
- Efficient translocation and increased surface area available for the uptake of water from the soil, thus imparting drought tolerance to HYR lines. An increase in root dry weight (DW) under stress indicates remobilization of assimilates from shoot to root, and higher root biomass increases the plant’s ability to find less-available water and thus increased drought resistance.
- HYR is predominantly induced in panicles, at about three fold at pre-anthesis and 1.5-fold at post-anthesis under severe drought relative to well-watered conditions, which include the critical reproductive phases at which drought stress reduces cereal yield.
- Expression of the HYR gene enhances photosynthesis in rice. HYR promotes a vigorous root system. HYR regulates GY under normal and stress conditions. HYR regulates expression of genes in PCM and stress response.
Improvement of GY is the primary objective in breeding and improvement of cereal crops. GY in cereals such as rice is limited by environmental stresses such as drought and high temperature, which are also increasing due to climate-change effects.
Labs working on this gene
- Virginia Bioinformatics Institute, Virginia Tech, Blacksburg, Virginia 24061, USA.
- Department of Crop, Soil, and Environmental Sciences, University of Arkansas, Fayetteville, Arkansas 72701, USA.
- School of Plant, Environmental, and Soil Sciences, Louisiana State University Agricultural Center, Baton Rouge, Louisiana 70803, USA.
- Ambavaram M M R, Basu S, Krishnan A, et al. Coordinated regulation of photosynthesis in rice increases yield and tolerance to environmental stress[J]. Nature communications, 2014, 5.
- Chen Y, Xu D Q. Changes in leaf photosynthesis of transgenic rice with silenced OsBP-73 gene[J]. Photosynthetica, 2007, 45(3): 419-425.
- Uga Y, Sugimoto K, Ogawa S, et al. Control of root system architecture by DEEPER ROOTING 1 increases rice yield under drought conditions[J]. Nature Genetics, 2013, 45(9): 1097-1102.
- Waller F, Furuya M, Nick P. OsARF1, an auxin response factor from rice, is auxin-regulated and classifies as a primary auxin responsive gene[J]. Plant molecular biology, 2002, 50(3): 415-425.
- Devaiah B N, Karthikeyan A S, Raghothama K G. WRKY75 transcription factor is a modulator of phosphate acquisition and root development in Arabidopsis[J]. Plant Physiology, 2007, 143(4): 1789-1801.