Comparative transcriptomics reveals seasonal climate-driven secondary xylem development in Pinus massoniana

Conifers exhibit marked sensitivity to seasonal variation, demonstrating responsive adaptations to cyclical fluctuations in temperature, photoperiod, and precipitation. As a keystone conifer species in southern China, Pinus massoniana presents critical research value for elucidating wood formation mechanisms in conifers through investigations of its seasonal growth strategies and associated molecular regulation. In this study, the seasonal dynamics were systematically monitored in the xylem of mature P. massoniana , including cambial phenology, xylem development, with comparative analyses conducted on five representative samples via the Iso-Seq and RNA-Seq techniques. Our findings demonstrate that wood formation initiation/cessation, earlywood latewood transition, and xylem growth rates, exhibit precise synchronization with multiple meteorological factors. Transcriptomic profiling revealed comprehensive gene regulatory networks governing these phenological adaptations, encompassing starch and sucrose metabolism, flavonoid biosynthesis, phenylpropanoid biosynthesis, and wood formation-related gene clusters. Through coexpression network analysis, we identified pivotal transcription factors (TF) that mediate distinct molecular mechanisms underlying secondary xylem seasonal development cycling, offering critical insights for deciphering the cascade processes that coordinate conifer growth periodicity. PmbHLH1 was successfully cloned and overexpressed, resulting in a statistically significant enhancement of stem growth rate. This multilevel characterization of P. massoniana secondary xylem adaptation mechanisms to seasonal climatic variations advances our understanding of coniferous forest adaptation strategies in southern China. • Different meteorological factors influence the initiation, rate, and cessation of wood formation. • Unfavorable moisture conditions promote the transition from earlywood to latewood. • Starch and sucrose metabolism, phenylpropanoid biosynthesis, and flavonoid biosynthesis undergo dramatic changes during the seasonal cycle. • Overexpression of PmbHLH1 accelerates the growth rate of xylem.