Environmental responsiveness of flowering time in cassava genotypes and associated transcriptome changes

Abstract

Cassava is an important food security crop in tropical regions of the world. Cassava improvement by breeding is limited by its delayed and poor production of flowers, such that cassava flowering under field conditions indirectly lengthens the breeding cycle. By studying genotype and environment interaction under two Nigerian field conditions (Ubiaja and Ibadan) and three controlled temperature conditions (22°C/18°C, 28/24°C and 34/30°C (day/night)), we found that while early flowering genotypes flowered at similar times and rates under all growing conditions (unfavorable and favorable field and controlled-temperature environments), late flowering genotypes were environmentally sensitive such that they were substantially delayed in unfavorable environments. Flowering times of late genotypes approached the flowering time of early flowering genotypes under relatively cool Ubiaja field conditions and in growth chambers at 22°C, whereas warmer temperatures elicited a delaying effect. Analysis of field and controlled temperature transcriptomes in leaves revealed that conditions that promote early flowering in cassava have low expression of the flowering repressor gene TEMPRANILLO 1 (TEM1), before and after flowering, among others. Field transcriptomes showed that the balance between flower promoting and inhibitory signaling, appeared to correlate with flowering time across the environments and genotypes.

Long-day photoperiod and cool temperature induce flowering in cassava: Expression of signaling genes

“…Previous anecdotal evidence suggests that extended photoperiod is more effective at cooler temperatures (Pineda et al, 2020a), and previous growth chamber trials indicated cool temperature is favorable for flowering (Adeyemo et al, 2019;Oluwasanya D. N. et al, 2021). Our results substantiate that cassava breeders aiming to utilize extended photoperiod to produce more flowers would benefit from utilizing locations with cooler temperatures.…”

“…Several other regulatory networks have been shown to interact with the SPL/miR172 module and affect the time to flowering, including those involving the plant hormone GA, GI (the core regulatory component of the circadian pathway) (Wang, 2014) and TEMs (Aguilar-Jaramillo et al, 2019). In both field and greenhouse experiments involving temperature, Oluwasanya D. N. et al (2021) found that expression of TEM2 in cassava was consistent with a role in regulating flowering. Our results did not show significant differentially expressed genes related to these pathways but they cannot be ruled out.…”

“…In previous study, plant growth regulator (PGR) treatments with the anti-ethylene silver thiosulfate (STS) and cytokinin were found to be effective tools in stimulating flower proliferation and feminization of flower development in cassava (Hyde et al, 2020; and cytokinin stimulates female flower proliferation in Jatropha (Chen et al, 2014(Chen et al, , 2019Froeschle et al, 2017). A previous study of the effect of temperature on flowering in cassava identified differentially expressed genes in several hormone pathways (Oluwasanya D. N. et al, 2021). Collectively, these studies have revealed that application of these hormones stimulates expression in a wide range hormone pathways.…”

“…Similarly, studies that involved evaluating flowering over a 1-year time-frame have led researchers to conclude that cassava responds to long days (Souza et al, 2020). More recently, studies in controlled environments have shown that cassava flowering is indeed induced in long days, but also by cool temperatures (22 • C) (Adeyemo et al, 2019;Oluwasanya D. N. et al, 2021).…”