Doubling Chromosomes Turns Goji Relative Self-Fertile by Disarming Its Own Pollen Rejection System

When plants duplicate their entire genome, the consequences ripple through nearly every aspect of their biology, from the size of their cells to the chemistry of their fruits. A new study in Plant Cell Reports adds a striking entry to that list: researchers report that chromosome doubling in Lycium chinense, a close relative of the goji berry, is associated with a dramatic relaxation of the plant’s self-incompatibility system, the genetic gatekeeping mechanism that normally blocks pollen from fertilizing its own flowers. In the autotetraploid plants, self-pollen tubes that would ordinarily stall in the upper reaches of the style instead pushed through toward the ovary, and the compatibility index—a quantitative measure of successful self-fertilization—climbed from 0.50 to 5.70, while fruit set after self-pollination surged from just 8.33 percent to 73.33 percent.

The findings, from a team led by Zixuan Wang and Jinhuan Chen at Beijing Forestry University together with Ken Qin of the National Wolfberry Engineering Research Center in Ningxia, tackle a long-standing puzzle in reproductive biology. Many flowering plants in the Solanaceae family, which includes tomato, potato, petunia, and Lycium, deploy gametophytic self-incompatibility, a system built around cytotoxic S-RNase proteins secreted by the pistil. These ribonucleases enter pollen tubes and destroy non-self pollen, but pollen carrying matching S-alleles is rejected through mechanisms that remain incompletely understood. How this system weakens or collapses in polyploid lineages has been debated for decades, and the new work offers one of the most detailed cytological and transcriptomic pictures to date of what changes when a diploid plant is converted to a tetraploid.

The team began with controlled morphological and cytological comparisons between diploid and autotetraploid L. chinense lines. Chromosome doubling left a visible signature throughout the reproductive apparatus: flowers enlarged, stigma receptivity persisted for a longer window, and pollen grains grew larger, although the altered ploidy also reshaped pollen performance and the dynamics of pollen tube extension. These traits matter commercially as well as scientifically, because stigma receptivity and pollen viability set the ceiling on how reliably a crop sets fruit, and because chromosome doubling has previously been shown by the same group to enhance biomass and carotenoid content in this species.

The decisive experiment involved tracking pollen tubes after self-pollination. In diploid plants, self-pollen tubes arrested in the upper style, the classic cytological hallmark of active rejection under gametophytic self-incompatibility. In the autotetraploids, however, self-pollen tubes continued growing through the style, a shift that translated directly into seed set. Controlled pollinations confirmed that the tetraploids produced vigorous seeds from self-fertilization, and analyses of seed vigor supported the conclusion that these were healthy, viable offspring rather than developmental accidents. The authors interpret this as a ploidy-associated transition toward self-compatibility, echoing reports from apple, Petunia, and wild tomato, where tetraploid lines have similarly shown relaxed rejection of their own pollen.

Historical explanations for this phenomenon trace back to Lewis’s work in the 1940s on competitive interactions between S-alleles in diploid pollen. Under gametophytic self-incompatibility, each haploid pollen grain expresses a single S-haplotype, and pollen matching the pistil is recognized and rejected. A diploid pollen grain, as occurs in tetraploids, carries two S-haplotypes, and the so-called heteroallelic pollen effect is thought to interfere with the rejection machinery. The new study situates L. chinense within this framework, proposing that heteroallelic pollen effects contribute to the failure of self-pollen rejection in the tetraploid, though the authors are careful to present this as part of a working model rather than a settled mechanism.

To probe the molecular side of the transition, the researchers sequenced transcriptomes from an unusually comprehensive sampling design: 72 pistil samples spanning the stigma, style, and ovary tissues at four pollination stages, in both ploidy levels. This spatiotemporal design revealed extensive transcriptional remodeling between diploids and tetraploids that was strongly dependent on both tissue and time. Temporal clustering and ploidy-by-time interaction analyses showed that the divergence was most pronounced in the stigma and the style, with the style exhibiting the strongest interactive response—precisely the tissue where the cytological difference in pollen tube arrest was observed. The ovary showed a distinct pattern, consistent with its role in later stages of the fertilization program.

Weighted gene co-expression network analysis then organized thousands of genes into tissue-associated modules, and the functional enrichments were telling. Membrane trafficking, phosphatidylinositol signaling, endocytosis, SNARE-mediated vesicular transport, and ubiquitin-mediated protein turnover all featured prominently. Each of these processes has a plausible role in the self-incompatibility story. In related Solanaceous systems, S-RNase must be compartmentalized within pollen tubes, and studies in Nicotiana have shown that the spatial sequestration of S-RNase, together with the stability of the HT-B protein, determines whether rejection succeeds. Endocytosis and vesicular trafficking are the natural suspects for altered S-RNase compartmentalization, while ubiquitin-mediated degradation pathways have been implicated in the controlled destruction of both S-RNase and its cofactors in self-incompatible Petunia.

The study also tracked the expression of known gametophytic self-incompatibility-related homologs, including LcS-RNase, LcHT-B, Lc120K, LcStEP, LcSBP1, and LcSKP1. These genes displayed distinct spatiotemporal expression patterns between the two ploidy levels, suggesting that the entire pollen-pistil dialogue is rewired after chromosome doubling rather than simply switched off. HT-B and the 120-kilodalton glycoprotein are required for S-specific pollen rejection in Nicotiana, NaStEP acts as a positive regulator of HT-B stability in pollen tubes, and SBP1 and SKP1 components connect the system to ubiquitin ligase machinery, so shifts in their coordinated expression could plausibly weaken the pistil’s ability to execute rejection. Integrating the cytology and the transcriptomics, the authors propose that heteroallelic pollen effects, altered S-RNase trafficking and compartmentalization, and changes in protein turnover may jointly reduce the cytotoxic impact of S-RNases, allowing self-pollen tubes to survive their journey through the tetraploid style.

For breeders, the implications are immediate. Goji berries and their relatives are economically important functional food crops, and self-incompatibility imposes a dependence on cross-pollinators and compatible S-genotype combinations that complicates orchard design and seed production. If chromosome doubling reliably confers self-fertility, autotetraploid Lycium lines could be propagated and bred with far fewer pollination constraints, while also benefiting from the enlarged organs and enhanced carotenoid content already documented in this species. The authors frame their findings as a cytological and transcriptomic framework for understanding ploidy-associated breakdown of gametophytic self-incompatibility, with direct relevance to polyploid breeding programs in Lycium and, by extension, to other S-RNase-based crops such as apple, pear, and potato where tetraploid self-compatibility has been observed or engineered.

The study also speaks to a broader evolutionary question: why polyploidy has been so successful in flowering plant history. Self-incompatibility breakdown is often cited as a reproductive assurance mechanism that could help new polyploids escape the mate-limitation problem, since a rare tetraploid emerging in a diploid population would struggle to find partners with matching ploidy. The L. chinense data provide a mechanistic bridge for that hypothesis, showing that a single genome-doubling event is associated with a cascade of changes in organ size, pollen behavior, pistil gene expression, and vesicular trafficking pathways that collectively transform a self-sterile plant into a largely self-fertile one. As genome editing tools make it increasingly feasible to knock out individual self-incompatibility components, as demonstrated with CRISPR-based disruption of HT-B and S-RNase in potato, the transcriptional landscape mapped in this study offers a catalog of candidate nodes for engineering self-fertility—and a reminder that sometimes the most efficient engineer is evolution itself, doubling the genome and letting the cell’s own logistics do the rest.

Subject of Research: Ploidy-associated breakdown of gametophytic self-incompatibility and pollen-pistil transcriptomic remodeling in autotetraploid Lycium chinense

Article Title: Chromosome doubling is associated with enhanced self-compatibility and transcriptional remodeling of pollen–pistil interactions in Lycium chinense

Article References: Wang, Z., Qin, Y., Qin, K., Zhang, B., & Chen, J. (2026). Chromosome doubling is associated with enhanced self-compatibility and transcriptional remodeling of pollen–pistil interactions in Lycium chinense. Plant Cell Reports, 45(10), Article 303. https://doi.org/10.1007/s00299-026-03991-7

Image Credits: AI Generated

DOI: 10.1007/s00299-026-03991-7

Keywords: Lycium chinense, autotetraploid, polyploidy, self-incompatibility, self-compatibility, S-RNase, pollen-pistil interactions, transcriptomics, pistil, pollen tube growth, goji berry, plant breeding