Flowering-time regulation by the circadian clock:From Arabidopsis to crops

Precise timing of flowering in plants is critical for their growth and reproductive processes.One factor controlling flowering time is the cycle of light and darkness within a day,known as the photoperiod.Plants are classified into long-day,short-day,and day-neutral plants based on light requirements for floral initiation.Although the molecular mechanisms that govern this differentiation remain incompletely understood,studies have consistently shown that the circadian clock plays a central role in regulating photoperiod response across diverse plant species.However,there is a scarcity of reviews describing the regulatory network linking the circadian clock with photoperiodic flowering.This review summarizes that regulatory network,focusing on the distinct roles of clock genes in long-day and short-day plants.We also discuss the strategies of clock gene mutations contributing to geographic variation in longday and short-day crops.

Heterosis Expression of Hybrid Rice in Natural-and Short-Day Length Conditions

Development of hybrid rice is an important strategy to increase yields of irrigated rice in China. Day length is a highly important environmental factor for hybrid rice adaptability, productivity and quality. Heterosis of hybrid rice has been utilized under natural- （long） day length conditions in the middle and lower reaches plain of Yangtze River Valley in China for a long time. However, whether the hybrid rice can show heterosis under short-day length conditions is unknown. In this study, we analyzed plant height, grain number per panicle, and other yield related traits of hybrid rice Liangyoupeijiu （LYP9） and its parents （Pei＇ai 64S and 93-11） under natural- and short-day length conditions and compared the respective heterosis. Results showed that earlier heading, reduced plant height, and reduced grain number per panicle were found in these three varieties under short-day length conditions relative to those under natural-day length conditions. In either natural- or short-day length conditions, heterosis of LYP9 was mainly displayed in grain number per panicle and plant height. This study may help in breeding and selectina suitable hybrid rice for different re qions with natural- or short-day length.

Short-day treatment during the growing period limits shoot growth and increases frost hardiness of hybrid aspen plants in the nursery

In Finland, under nursery conditions hybrid aspen may continue their shoot growth until early September. Thus, frost hardening is usually delayed. To solve this problem, we used a three-week period of short-day （SD） treatment between late July and mid-August. During autumn after frost exposure, frost hardiness （FH） was assessed three times with a stem-browning test. The resuits showed that after SD treatment shoot growth ceased and FH increased when compared to untreated hybrid aspen. Furthermore, the height of SD-treated hybrid aspen varied much less than that of the control plants. We conclude that SD treatment in the nursery during the growing period can be used as a supplementary method for producing well-hardened and uniform hybrid aspen plants.

Climate,female traits and population features as drivers of breeding timing in Mediterranean red deer populations

Understanding the factors that lead to variation in the timing of breeding in widespread species such as red deer(Cervus elaphus)is crucial to predict possible responses of wild populations to different climate scenarios.Here,we sought to further understand the causes of inter-annual variation in the reproduction timing of female deer in Mediterranean environments.An integrative approach was used to identify the relative importance of individual,population and climate traits in the date of conception of free-ranging deer,based on a dataset of 829 hinds culled during 12 years.We found that a population trait,density,was the most important factor explaining the variation in conception dates,with greater densities causing later conception dates.Body mass was the second in importance,with heavier females conceiving earlier than lighter ones.Almost equally important was the spring real bioclimatic index,a measure of plant productivity,causing later conception dates in the least productive springs(drier and hotter).Another climatic component,the end of summer drought,showed that the sooner the autumn arrives(greater rainfalls and cooler temperatures)the earlier the conception dates.Interestingly,age class was found to be a minor factor in determining conception date.Only older females(≥10 years old)conceived significantly later,suggesting reproductive senescence.This study highlights not only the importance of population and individual traits but also the influence of climatic parameters on the deer reproductive cycle in Mediterranean environments,giving valuable insight into how reproductive phenology may respond to seasonality and global climate changes.