In order to induce unreduced pollens, microsporogenesis and male flower bud (MFB) development were compared in rubber tree clone RRIM 600. We observed strong asynchronism in different MFBs in an inflorescence. Asynchronism of microsporogenesis in different microsporangiums from a MFB was also observed. The relationship between microsporogenesis and external morphology was examined, which was used to estimate microsporogenesis stages of MFBs. Unreduced pollen was successfully induced by high temperature exposure in this study, with the highest production ratio of about 20.17% at 44 °C. Our findings showed that diplotene to metaphase I may be the most effective stage for unreduced pollen induction, and 42–44 °C may be the suitable treatment temperature in rubber trees. Thus, microsporogenesis of MFBs has been elucidated in detail in the rubber tree clone RRIM 600 and will provide a reference for future breeding studies of rubber trees.

Eight triploids were screened among offspring of the rubber tree clone GT1 × different clones by flow cytometry and chromosome counting. Twenty-five simple sequence repeat (SSR) markers were screened to identify the origin of 2n gametes, to determine the male parents of these triploids, and to evaluate the mechanism of 2n gamete formation using band configurations and microsatellite DNA allele counting peak ratios (MAC-PR). The results showed that 2n gametes originated from the maternal rubber tree clone GT1, contributing the extra genome copy present in the triploids. It was confirmed that GT1 is able to produce a 2n megagametophyte spontaneously. Many male parents were shown to provide pollen for formation of triploid rubber trees, including clones RRIC 103, Yunyan 277-5, and three other clones. The second division restitution (SDR) was likely the main mechanism involved in formation of megagametophytes in GT1, as the rate of maternal heterozygosity restitution (HR) of all eight triploids varied from 27.78% to 75.00%, with a mean of 51.46%, and all 25 markers varied from 0% to 100%, with a mean of 51.69%. Elucidation of the origin and formation of 2n gametes will help optimize further sexual hybridization of polyploid rubber trees.

Polyploid breeding is important in Populus genetic improvement programs because polyploid trees generally display increased height growth compared to their diploid parents. However, the genetic mechanism underlying this phenomenon remains unknown. In the present study, apical bud transcriptomes of vigorous, fast growing Populus allotriploid progeny genotypes and their diploid parents were sequenced and analyzed. We found that these allotriploids exhibited extensive transcriptomic diversity. In total, 6020 differentially expressed genes (DEGs) were found when the allotriploid progeny and their parents were compared, among which 791 overlapped between the allotriploids and both parents. Many genes associated with cell differentiation and meristem development were preferentially expressed in apical buds of the fast growing Populus allotriploids compared to their diploid parents. In addition, many auxin-, gibberellin-, and jasmonic acid-related genes were also preferentially expressed in the allotriploids compared to their parents. Our findings show that allotriploidy can have considerable effects on duplicate gene expression in Populus. In particular we identified and considered DEGs that provide important clues for improving our mechanistic understanding of positive heterosis of vigor- and growth-related traits in Populus allotriploids.

NAC (NAM, ATAF, and CUC) transcription factors are essential in regulating plant stress response and senescence, with their functions being modulated by alternative splicing. The molecular mechanisms of stress-induced premature flowering and drought tolerance in Phyllostachys edulis (moso bamboo) are not yet fully understood. In this study, a novel NAC variant derived from PheNAC23, named PheNAC23^ES, was isolated. PheNAC23^ES exhibited distinct expression patterns compared to PheNAC23 during leaf senescence and drought stress response. Overexpression of PheNAC23 promoted flowering and reduced its tolerance to drought stress in Arabidopsis thaliana (A. thaliana). However, overexpression of PheNAC23^ES exhibited the opposite functions. PheNAC23 was localized in the nucleus and had transactivation activity, while PheNAC23^ES had a similar localization to the control green fluorescent protein and no transactivation activity. Further functional analysis revealed that PheNAC23^ES could interact with PheNAC23, suggesting that PheNAC23^ES might serve as a small interfering peptide that affects the function of PheNAC23 by binding to it.