Comparison of red raspberry and wild strawberry fruits reveals mechanisms of fruit type specification

Authors: ZHOU, JUNHUI - University Of Maryland; LI, MUZI - University Of Maryland; LI, YONGPING - The Chinese University Of Hong Kong (CUHK); XIAO, YUWEI - University Of Maryland; LI, XI - University Of Maryland; GAO, SHENGLAN - Peking University; SADOWSKI, NORAH - Johns Hopkins University; TIMP, WINSTON - Johns Hopkins University; Dardick, Christopher; Callahan, Ann; MOUNT, STEPHEN - University Of Maryland; LIU, ZHONGCHI - University Of Maryland

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/2023
Publication Date: 7/13/2023
Citation: Zhou, J., Li, M., Li, Y., Xiao, Y., Li, X., Gao, S., Sadowski, N., Timp, W., Dardick, C.D., Callahan, A.M., Mount, S., Liu, Z. 2023. Comparison of red raspberry and wild strawberry fruits reveals mechanisms of fruit type specification. Plant Physiology. 193(2):1016-1035. https://doi.org/10.1093/plphys/kiad409.
DOI: https://doi.org/10.1093/plphys/kiad409

Interpretive Summary: Fruits such as strawberry, raspberry, apple, and peach develop very differently from each other. A ‘true’ fruit such as raspberry or peach forms the fleshy edible part from the flower ovary. In contrast, the edible parts of strawberries or apples form from the base of the flower called the receptacle or hypanthium, respectively. Here we aimed to study how these different fruit developmental strategies are controlled at the genetic and molecular level by comparing gene activity in developing strawberry and raspberry fruits. Both fruit types have what are called ‘compound’ flowers and produce many seeds within each fruit. Strawberrys are unique in that the seeds are distributed on the surface of the swollen receptacle while raspberries develop a cluster of ‘druplets’ that separate from the receptacle. The data showed that strawberry ovaries undergo a lignification or drying process early during fruit development leading to the dry seeds dispursed on the surface. In contrast, the ovaries in raspberries display gene expression patterns consistent with fleshy fruit development. Differences were also found in the gene activity within the receptacle tissues leading to the identification of a several potential regulators of these different fruit development programs. Collectively the data shows how plants have evolved different reproductive strategies and provide key gene targets for future genetic improvement of fruit crops.

Technical Abstract: Belonging to the Rosaceae family, raspberry and strawberry are closely related species with distinct fruit types. While the numerous ovaries become the juicy fruits in raspberry, their strawberry counterparts become dry and tasteless achenes. In contrast, while the strawberry receptacle, the stem tip, enlarges to become a red fruit, the raspberry receptacle shrinks and dries. The distinct fruit-forming ability of homologous organs in these two species allows us to investigate fruit type evolution. We assembled and annotated the genome of red raspberry Rubus idaeus and characterized its fruit development morphologically and physiologically. Subsequently, transcriptomes of dissected and staged raspberry fruit tissues were compared to those of strawberry fruit tissues from a prior study. The comparison showed that class B MADS box gene expression is negatively correlated with fruit-forming ability, suggesting a conserved inhibitory role of B class genes for fruit formation. Additionally, the inability of strawberry ovaries to develop into fruit flesh was correlated with highly expressed lignification genes and extensive lignification of the ovary pericarp. Our work provides extensive genomic resources as well as several potential mechanisms underlying fruit type specification. These findings provide the framework for understanding the evolution of different fruit types, a defining feature of angiosperm.lick or tap here to enter text.