Engineering parthenocarpic fruit production in tomato

Abstract

Normally, fruits are formed only following fertilization. In tomato, fertilization is sensitive to extreme temperatures, resulting in reduced yield. Yield stability would therefore benefit from tomato varieties with parthenocarpic fruits, which develop independently of fertilization. The objective of the research was to generate parthenocarpic tomato lines by mutating PRC2 components, to investigate how PRC2 and auxin signaling regulate fruit initiation and growth, and to generate parthenocarpic lines for breeding. We reasoned that heterozygous prc2 mutations would generate parthenocarpic fruits with minimal vegetative effects, as they act in the female gametophyte. The specific objectives were : To generate (1) tomato PRC2 mutants and characterize them developmentally (2) and molecularly (3), and to test their performance in the field (4). Aim 1 proved challenging, and was achieved only during the third year. Therefore the research was extended for an additional 8 months, during which goals 2 and 4 were achieved. The research yielded mutations in 4 different PRC2 components, two of which were loss-of-function mutations that produced parthenocarpic fruits, Slfie and Slmsi1 mutants. Characterization of heterozygote Slfie mutants showed that they produce fruits independently of fertilization across a range of growth conditions. No homozygote Slfie mutants were obtained, likely due to failure of the mutant allele to transfer via the female gametopyte. Slfie/+ fruits were of good quality in contrast to most previously described parthenocarpic fruits. Initial characterization under heat stress showed a dramatic increase in yield under extreme heat, therefore providing yield stability. In addition, we characterized single and double mutants in tomato SlARF8a and SlARF8b, and found that these also gave plants with parthenocarpic fruit growth and increased yield stability. The research yielded genetic material that can be used in breeding programs to increase yield stability under unstable climate