Auxin plays essential roles in plant normal growth and development. The auxin signaling pathway relies on the auxin gradient within tissues and cells, which is facilitated by both local auxin biosynthesis and polar auxin transport (PAT). The TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS (TAA)/YUCCA (YUC) pathway is the most important and well-characterized pathway that plants deploy to produce auxin. YUCs function as flavin-containing monooxygenases (FMO) catalyzing the rate-limiting irreversible oxidative decarboxylation of indole-3-pyruvate acid (IPyA) to form indole-3-acetic acid (IAA). The spatiotemporal dynamic expression of different YUC gene members finely tunes the local auxin biosynthesis in plants, which contributes to plant development as well as environmental responses. In this review, the recent advances in the identification, evolution, molecular structures, and functions in plant development and stress response regarding the YUC gene family are addressed.

The initiation and induction of root primordia are of great importance for adventitious root (AR) formation in cutting propagation of horticultural and forestry crops. However, the underlying mechanisms orchestrating these early phases of AR formation remain largely unexplored. Here, we investigated the physiological and transcriptomic changes during the early AR phases in mulberry stem hardwood cuttings. The results showed that the concentrations of soluble proteins increased, whereas concentrations of soluble sugars and starch were decreased. Indole-3-acetic acid (IAA) and zeatin had a rapid transit peak at 6 h after planting (hAP) and declined thereafter. The activities of peroxidase and catalase persistently increased and indole-3-acetic acid oxidase was maintained at a higher stable level from 0 hAP, while the activities of polyphenol oxidase fluctuated with soluble phenolics and IAA levels. The comparative transcriptome identified 4276 common genes that were differentially regulated at −6, 0 and 54 hAP. They were separated into five clusters with distinct biological functions such as defense response and photosynthesis. Considerable common genes were assigned to pathways of sugar metabolism, mitogen-activated protein kinase, and circadian rhythm. The gene co-expression network analysis revealed three major co-expressed modules involved in stress responses, hormone signaling, energy metabolism, starch metabolism, and circadian rhythm. These findings demonstrate the positive effect of auxin on AR induction, and uncovered the crucial roles of stress responses, hormone signaling and circadian rhythm in coordinating the physiological changes during the early phases of AR formation in mulberry stem hardwood cuttings.

Cotton fibers provide an important source of raw materials for the textile industry worldwide. Cotton fiber is a kind of single cell that differentiates from the epidermis of the ovule and provides a perfect research model for the differentiation and elongation of plant cells. Cotton fiber initiation is the first stage throughout the entire developmental process. The number of fiber cell initials on the seed ovule epidermis decides the final fiber yield. Thus, it is of great significance to clarify the mechanism underlying cotton fiber initiation. Fiber cell initiation is controlled by complex and interrelated regulatory networks. Plant phytohormones, transcription factors, sugar signals, small signal molecules, functional genes, non-coding RNAs, and histone modification play important roles during this process. Here, we not only summarize the different kinds of factors involved in fiber cell initiation but also discuss the mechanisms of these factors that act together to regulate cotton fiber initiation. Our aim is to synthesize a systematic and comprehensive review of different factors during fiber initiation that will provide the basics for further illustrating these mechanisms and offer theoretical guidance for improving fiber yield in future molecular breeding work.

The NAC (NAM/ATAF1/2/CUC2) transcription factors are pivotal regulators in plant development and stress responses. Despite the extensive studies on the NAC gene family across various plant species, the characterization of this gene family in mulberry (Morus atropurpurea) remains unexplored. Here, we conducted a genome-wide identification and characterization of the NAC gene family in M. atropurpurea. A total of 79 MaNAC genes were identified and classified into 20 subgroups, displaying an uneven distribution across the 14 chromosomes. The structural analysis found that most MaNAC genes possess at least three exons and contain the conserved NAC domain and characteristic motifs at the N-terminus. Eleven collinear gene pairs were identified in M. atropurpurea genome. Interspecies collinearity analysis demonstrated a closer evolutionary relationship between M. atropurpurea and Populus trichocarpa, supported by the identification of 116 collinear gene pairs. Expression profiling revealed dynamic changes in the transcript levels of most MaNAC genes during mulberry fruit maturation. Notably, the eight MaNAC members from the OsNAC7 subfamily exhibited tissue-specific expression patterns. A significant proportion of MaNAC genes displayed varying degrees of responsiveness to drought stress and sclerotium disease. MaNAC12, MaNAC32, MaNAC44 and MaNAC67 emerged as the most highly responsive candidates. Overexpression of MaNAC69 enhanced drought tolerance in Arabidopsis. These findings provide a robust foundation for future functional studies and mechanistic investigations into the roles of the NAC gene family in M. atropurpurea, offering insights into their contributions to development and stress adaptation.

Xylem plasticity is important for trees to coordinate hydraulic efficiency and safety under changing soil water availability. However, the physiological and transcriptional regulations of cambium on xylem plasticity are not well understood. In this study, mulberry saplings of drought-resistant Wubu and drought-susceptible Zhongshen1 were subjected to moderate or severe drought stresses for 21 days and subsequently rewatered for 12 days. The anatomical, physiological and transcriptional responses in wood and cambium were analyzed. Most parameters were not affected significantly under moderate drought for both cultivars. Severe drought led to decreased vessel lumen diameter and increased vessel frequency, increased starch and hemicellulose in wood of both cultivars. Notably, increased soluble sugars and lignin were detected only in wood of Wubu. In cambial zone, levels of starch, glucose, fructose, mannose and cytokinin were decreased in both cultivars, whereas soluble sugars were increased in Wubu but deceased in Zhongshen1. RNA-sequencing identified 1824 and 2471 differentially expressed genes in Wubu and Zhongshen1 under severe drought, respectively. These responses were partially recovered after rewatering. Weighted gene correlation network analysis identified modules of co-expressed genes correlated with the anatomical and physiological traits of wood and cambium, with the turquoise and green modules most strongly correlated with traits under drought or rewatering. These modules were enriched in gene ontology terms related to cell division, cytoskeleton organization, cell wall modification, dark respiration, vesicle transport and protein metabolism. Detailed gene expression patterns indicate that reprogramming of cambium activity was relatively similar in both cultivars, but at different scales. These findings provide important insights into the physiological and molecular mechanisms underlying xylem plasticity based on cambium and offer valuable references for breeding drought-resistant mulberry and other woody species in light of future drier climate scenarios.