Jan Leach received her BS and MS degrees in microbiology from the University of Nebraska in 1975 and 1977, respectively, and her PhD in plant pathology from the University of Wisconsin in 1981. She was a postdoctoral fellow at East Malling Research in Kent, United Kingdom, before joining Kansas State University as an assistant professor in 1984; she was recognized as a University Distinguished Professor at Kansas State in 1998. Leach moved to Colorado State University (CSU) in 2004 and was recognized as a University Distinguished Professor in 2007. She has served as the research associate dean for the CSU College of Agricultural Sciences since 2015.
Leach has served APS and associated societies in many capacities. She was the editor-in-chief of MPMI (1998–2000) and the president of IS-MPMI (1999–2001), APS (2006–2007), and ISPP (2018–2023). She is also a fellow of APS, AAAS, and AAM. In 2018, she won the prestigious Agropolis Foundation Louis Malassis International Scientific Prize for Agriculture and Food for Distinguished Scientist. She is a co-editor of Annual Review of Phytopathology, a member of the Board on Agriculture and Natural Resources for the National Academy of Sciences, and a nonresident fellow of the Noble Foundation. She recently finished two terms on the U.S. National Science Advisory Board for Biosecurity, and she has served in expert advisory roles for institutions in China, Japan, and Korea.
Leach has devoted her 30-year career to understanding how to stabilize disease resistance in rice to reduce crop losses. The impact of her work is increased by her ability to collaborate with international scientists in diverse fields. She has worked on more than 160 peer-reviewed publications; more than 110 of those publications included international collaborations with plant and microbial biologists, entomologists, computational biologists, and other professionals ranging from computer modelers to social scientists. Notably, Leach's work provided the first rational approach to predicting R gene durability prior to introgression and deployment. She was the first to identify TAL effectors in Xanthomonas oryzae and to demonstrate that each TAL effector was recognized by a different R gene. She also provided the first experimental validation that TAL effectors differed in their contribution to pathogen virulence and pathogen fitness, and that this correlated with the durability of the corresponding R genes in the field. This discovery enables prediction of the durability of plant resistance genes before breeders spend years to introduce them into favorite cultivars. Leach's team demonstrated that the basis for differences in contributions of some defense response genes to effective disease resistance QTL was at the expression level and identified the promoter changes controlling their contribution to QTL function. She and her collaborators demonstrated that accumulation of QTL containing candidate defense response genes resulted in long-lasting resistance in the field, for example, for more than 24 continuous cropping seasons in an area with intense rice blast pressure in China.
Leach's discoveries in avr-R gene interactions range from understanding of evolution of disease resistance to identifying effector gene function. Leach and collaborators were the first to demonstrate that R genes function in interspecific transfers, that is, maize Rxo1 functions in rice, even though rice diverged from maize more than 50 million years ago. Leach's team showed that Rxo1 recognizes a bacterial effector protein encoded by the avrRxo1 gene, and that genes related to avrRxo1 are present in at least three different bacterial genera. They also discovered that AvrRxo1 is a toxin that bacteria use to control their own population growth and as a toxin in plant cells. The broad family of bacterial AvrRxo1-like proteins have potential as antibiotics and in therapies for cancer.
Leach's work will enable prediction of a crop's resilience to combined stresses of disease and high temperatures prior to deployment. Leach and her collaborators discovered that the R gene, Xa7, confers higher levels of resistance at high versus low temperatures, while the opposite is true for most other bacterial blight R genes. Unlike other resistance genes, Xa7 was highly effective in a study spanning 22 cropping seasons of field assessments. The greater efficacy of Xa7 in the hot season was related to slowed evolution of the pathogen population to virulence. This information on why plants are more susceptible to disease at high temperatures provides critical pieces of information that will guide future crop improvement strategies, particularly in the face of a changing climate.
Leach has had a substantial impact on mentoring women scientists. She has mentored 22 PhD, 13 MS students, 23 post-docs, 20 visiting scientists, and numerous undergraduate students. In 2015, Leach became a co-coordinator for the Rice: Research to Production (RiceR2P) course at IRRI, a course that provides researchers with a global vision of science, innovation in outreach, education and public service, and connects them to the international community. More than 250 early career scientists from 45 countries have participated and, of these, 68% were women. In addition to this, many women who are currently in leadership positions in plant pathology around the world consider Leach an essential career mentor. Her impact in mentorship is global and has not yet been formally recognized and it is one of the factors that make her distinct among APS fellows.
Leach is widely recognized for leadership in grand challenges in agriculture. Her leadership is another attribute that makes Leach distinct among plant pathologists and APS fellows. She is the only person who has led APS, IS-MPMI, and ISPP. In addition, she served on the APS Public Policy Board for 16 years and through this, she led the launch of the Phytobiomes Initiative. This advocacy plan convened international groups of scientists with diverse expertise to develop a roadmap to address the global grand challenges and ensure food security for the future. A Roadmap for Phytobiomes Research and Translation was endorsed by 24 different scientific societies, government agencies and industries at its launch. This initiative led to the launch of a new journal, called Phytobiomes, and the organization of the International Phytobiomes Alliance.