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The morphological characteristics of metamorphosis in stamens of Anemone barbulata Turcz. were investigated using morphological and histological analyses. The results showed that stamens were transformed into either white sepaloid organs or more frequently green leaflike structures with successive variations. The extreme metamorphic stamen was represented as a three-lobed leaflike structure with a long stalk, highly consistent with the morphological characters of the normal leaves of the plant. It was hypothesized that the connective and two pollen sacs of the anther were transformed into the three lobes of the metamorphosed stamen, respectively. The depression and circinate stages were identified as the important and necessary processes in the transformation of stamens from axial to foliar organs, suggesting probably the alternative evolutionary process of the formation of anthers derived from foliar organs. The morphological traces of leaf, sepal, and carpel observed in the metamorphosed stamens suggested the homeotic transformations among these organs. The foliar stage in the ancestral stamens of angiosperms was reflected ontogenically in the metamorphosed stamens of A. barbulata. Our findings of a series of metamorphic stamens probably represent the morphological evidence to support the hypothesis that the flowers of angiosperms were derived from metamorphic leaves with the progressive development mode in the evolution of floral organs. [ABSTRACT FROM AUTHOR]

MicroRNAs (miRNAs) are small molecule RNAs widely involved in responses to plant abiotic stresses. We performed small RNA sequencing of cotton anthers at four developmental stages under normal and high temperature (NT and HT, respectively) conditions to investigate the stress response characteristics of miRNA to HT. A total of 77 miRNAs, including 33 known miRNAs and 44 novel miRNAs, were identified, and 41 and 28 miRNAs were differentially expressed under NT and HT stress conditions, respectively. The sporogenous cell proliferation (SCP), meiotic phase (MP), microspore release period (MRP), and pollen maturity (PM) stages had 10 (including 12 miRNAs), four (including six miRNAs), four (including five miRNAs), and seven (including 11 miRNAs) HT stress-responsive miRNA families, respectively, which were identified after removing the changes in genotype-specific miRNAs under NT condition. Seven miRNA families (miR2949, miR167, and miR160 at the SCP stage; miR156 and miR172 at the MP stage; miR156 at the MRP stage; and miR393 and miR3476 at the PM stage), which had expression abundance of more than 10% of the total expression abundance, served as the main regulators responding to HT stress with positive or negative regulation patterns. These miRNAs orchestrated the expression of the corresponding target genes and led to different responses in the HT-tolerant and the HT-sensitive lines. The results revealed that the HT stress response of miRNAs in cotton anthers were stage-specific and differed with the development of anthers. Our study may enhance the understanding of the response of miRNAs to HT stress in cotton anthers and may clarify the mechanism of plant tolerance to HT stress. [ABSTRACT FROM AUTHOR]