BBSRC-NSF/BIO: Anatomy and functions of LTP interactomes and their relationship to small RNA signals in systemic acquired resistance

Plants possess a unique form of immunity called systemic acquired resistance (SAR). SAR is highly desirable because it protects the whole plant against a wide range of pathogens and is long-lasting. When a primary pathogen infects the plant and activates SAR, mobile signals generated at the infection site travel to distal portions of the plant and prepare them to fend off future infections.

Several SAR-inducing factors, including some that move systemically, have been discovered, though the identity of the early SAR signal has remained elusive. In a recent breakthrough, we identified RNA-based molecules that function within the early time frame of SAR. This collaborative project between laboratories at the University of Kentucky and University of Warwick will combine computational, biochemical, gentics and metabolomic analyses to generate a deep mechanistic understanding of these molecules.

By facilitating the use of SAR in developing sustainable and environmentally friendly crop protection strategies, and its applicability to economically important crop species, this project will benefit US and UK agricultural economies. The knowledge gained could have rational applications in human health because the underlying components have conserved functions in mammalian physiology.

The project will generate undergraduate research experiences for Kentucky students from primarily underserved backgrounds, middle-high school workshops via the Kentucky Youth Science Summit, Girl Scout’s GEMS program, Science on the Hill public engagement series and undergraduate research-based experiential learning coursework.

This project will investigate early signals in Systemic Acquired Resistance (SAR). The production of the SAR mobile signal is thought to occur within 3 h of primary infection, and the infected leaf must remain attached for at least 4 h after inoculation for SAR to be induced, suggesting that the mobile signal is translocated during that early timeframe.

We find that two phased 21 nucleotide RNA (tasi-RNA) derived from Trans-Acting Small Interfering RNA3a (TAS3a), are synthesized within 3 h of pathogen infection, move to distal leaves within 4 h and function as the elusive early mobile signal in SAR. TAS3a cleaves Auxin Response Factor (ARF) 3 and conversely increased ARF3 negatively regulates SAR. TAS3a positively regulates the expression of Lipid Transfer Proteins (LTP) 3, 4 and AZI1 and a novel protein A70.

The LTPs form a complex and regulate SAR by promoting transport of tasi-ARFs. Systemic mobility of the LTPs further suggests that SAR activation is associated with the transport of a high molecular weight LTP-RNA complex. This project will characterize the LTP-RNA interactome and the dynamics of systemic activation of A70, and will compute how changes in these complexes regulate SAR.

In addition, we will characterize ARF3 targets and SAR-associated components that function downstream of tasi-ARFs and A70. Research findings will be disseminated to the scientific community via traditional publication routes, presentations at conferences, and through outreach to US soybean, corn, wheat, and oat growers via annual meetings and grower-targeted publications, as well as with vegetable and protected crop growers and seed companies in the UK.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.