Unraveling the Genetic Mechanisms Underlying Fruit Size and Sugar Content in Wax Apple

A recent study has successfully decoded the autotetraploid genome of the wax apple, uncovering its genetic evolution and key factors driving fruit diversity. The research highlights the fruit's rich antioxidant profile, with promising implications for human health and breeding strategies aimed at enhancing nutritional value.

Wax apple (Syzygium samarangense), known for its crisp texture, rose-like aroma, and health benefits, faces breeding challenges due to its complex genetic diversity and limited genomic data. These obstacles have hindered efforts to improve key fruit qualities such as size and sugar content. Addressing these issues requires comprehensive genomic research to unravel the genetic mechanisms underlying these traits.

Led by scientists from the Fujian Academy of Agricultural Sciences and Fujian Agriculture and Forestry University, this study (DOI: 10.1093/hr/uhad214) was published on October 25, 2023, in Horticulture Research. The research provides chromosome-scale genome and transcriptome data of the wax apple, focusing on genes that regulate fruit size, sugar metabolism, and male sterility. This pioneering work opens new possibilities for the molecular breeding of wax apple varieties with enhanced fruit characteristics.

The study assembled a 1.59 Gb genome, revealing three rounds of whole-genome duplication events in wax apple. Key genes influencing fruit size, including APETALA1 (AP1) and APETALA1 (AP2), were identified, which promote growth by regulating sepal development. For sugar content, elevated expression of sugar transporter genes such as Sugars Will Eventually be Exported Transporters (SWEETS) and Sucrose Transporters (SUTs) was linked to sweeter fruit varieties. Moreover, the research discovered that male sterility in certain varieties results from reduced expression of critical genes like DYSFUNCTIONAL TAPETUM1 (DYT1), TAPETUM DEVELOPMENT AND FUNCTION1 (TDF1), and ABORTED MICROSPORE (AMS), which are essential for tapetum development and pollen viability. This male sterility contributes to the formation of seedless fruits, a highly valued trait in the market.

"This research represents a major advance in understanding the genetic foundations of essential traits in wax apple," said Dr. Lihui Zeng, a co-author of the study.

The haplotype-resolved genome serves as a crucial resource for exploring genetic diversity and selective breeding, bringing us closer to creating superior wax apple varieties with improved size, sweetness, and seedlessness."

Dr. Lihui Zeng, Chinese Academy of Sciences

The insights gained from this study are expected to accelerate breeding programs focused on developing wax apples with enhanced fruit size, higher sugar content, and seedless traits, aligning with consumer demands. The findings also provide a valuable framework for improving other fruit crops facing similar breeding challenges, marking a significant step forward in the field of horticultural genomics.