Researchers led by Dr. WANG Bing and LI Jiayang from the Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences have revealed that the low phosphorus activates the biosynthesis and signaling of strigoalactones to regulate plant architecture and uptake of nitrogen and phosphate in rice.
The researchers have also developed transgenic plants with higher nutrient use efficiency, improved shoot- and root-architecture, and elevated biomass and grain yield under low- and medium-phosphrous conditions.
Phosphorus is one of the macroelements necessary for the growth and development of crops. The high yield of crops depends on the large input of chemical fertilizers such as phosphorus fertilizers, which increases crop yield while reducing the use efficiency of phosphorus. Phosphorus rock is a nonrenewable resource, and excessive production and application of phosphorus fertilizer have led to the waste of agricultural resources and environmental pollution, which is unfavorable for the sustainable development of agriculture. Therefore, it is important to explore the mechanisms of the low-phosphorus plant responses to improve phosphorus use efficiency, reduce phosphorus fertilizer application, and achieve the sustainable development of agriculture.
Strigolactones are a class of plant hormones that regulate various biological processes and play an important role in the response to phosphorus deficiency. Low-phosphorus stress significantly induces strigolactone biosynthesis in rice, but the transcription factors regulating this process have not been identified. The mechanisms by which strigolactone regulates key plant architecture and the balance of nitrogen and phosphorus in rice under low-phosphorus conditions remain unclear.
This study found that in the low-phosphorus environment, the rice phosphorus signaling core regulator OsPHR2 directly activates the expression of NSP1, NSP2 and strigolactone synthesis genes; NSP1 and NSP2 further form a heterodimer, which directly binds to and activates transcription of strigolactone synthesis.
Strigolactone further activates its signal pathway to inhibit tiller bud elongation and reduce lateral root density by promoting the expression of the negative tiller regulator OsTB1 and inhibiting CRL1 expression, respectively. Interestingly, they found that strigolactones inhibit nitrogen uptake and transport by regulating the expression of nitrogen transporter genes such as OsNRT2.1, OsNRT1.1B and OsNAR2.1 and promote phosphorus uptake by activating the expression of phosphorus transporter genes OsPTs. These results illustrate a new mechanism underlying the balance of nitrogen and phosphorus in rice.
Furthermore, they found that although overexpression of NSP1 and NSP2 with constitutive promoters led to reduced tiller number, panicle length and grain yield, overexpression of NSP1 and NSP2 with their own promoters performed appropriately elevated strigolactone biosynthesis and increased phosphorus absorption in a low-phosphorus environment. The NSP1p:NSP1 and NSP2p:NSP2 plants showed elevated nitrogen absorption, increasd tiller number, panicle length, biomass and grain yield per plant in low- and medium-phosphorus conditions.
In summary, the researchers revealed the regulatory mechanisms of strigolactone biosynthesis and roles of strigolactone signaling in adaption to low phosphorus environments. This study provides genetic resources and effective strategies for improving rice architecture and nutrient use efficiency under low phosphorus conditions and lays a solid foundation for the molecular design and breeding of high-yield and high-efficiency crops.
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