Genetic variation in yield under hot ambient temperatures spotlights a role for cytokinin in protection of developing floral primordia

Abstract

Unusually hot ambient temperatures (HAT) can cause preanthesis abortion of flowers in many diverse species, limiting crop production. This limitation is becoming more substantial with climate change. Flower primordia of passion fruit (Passiflora edulis Sims) vines exposed to HAT summers, normally abort. Flower abortion can also be triggered by gibberellin application. We screened for, and identified a genotype capable of reaching anthesis during summer as well as controlled HAT conditions, and also more resistant to gibberellin. Leaves of this genotype contained higher levels of endogenous cytokinin. We investigated a possible connection between higher cytokinin levels and response to gibberellin. Indeed, the effects of gibberellin application were partially suppressed in plants pretreated with cytokinin. Can higher cytokinin levels protect flowers from aborting under HAT conditions? In passion fruit, flowers at a specific stage showed more resistance in response to HAT after cytokinin application. We further tested this hypothesis in Arabidopsis. Transgenic lines with high or low cytokinin levels and cytokinin applications to wild-type plants supported a protective role for cytokinin on developing flowers exposed to HAT. Such findings may have important implications in future breeding programmes as well as field application of growth regulators.

Heat-Induced Cytokinin Transportation and Degradation Are Associated with Reduced Panicle Cytokinin Expression and Fewer Spikelets per Panicle in Rice

“…In rice, exogenous BAP application increased the abundance of tZ-type CTKs (Liu et al, 2011) and the number of spikelets per panicle (Ding et al, 2014). Similarly, several passion fruit species and Arabidopsis ecotypes that showed stable abundance of aCTKs had less severe reductions in floret number in comparison with species and ecotypes that showed reduced CTK abundance in response to high temperature when exogenous CTKs were applied to mitigate the effect of heat injury on floret growth (Sobol et al, 2014). Additionally, we observed that relative panicle CTK concentrations were positively correlated with the relative number of spikelets per panicle ( Figure 5A ).…”

“…In rice, Arabidopsis and passion fruit, reduced CTK abundance in shoots in response to heat caused floret abortion, whereas exogenous CTK application to shoots mitigated the effects of heat injury on branches and florets (Sobol et al, 2014; Wu et al, 2016). CTK transportation via xylem sap is involved in heat stress tolerance (Ha et al, 2012; Zwack and Rashotte, 2015).…”

The impact of heat stress targeting on the hormonal and transcriptomic response in Arabidopsis

“…Both exogenous application of CKs [10] and elevation of CK levels by overexpression of the biosynthetic gene isopentenyltransferase (ipt) under the senescence-inducible promoter (SAG12) resulted in elevation of HS tolerance [11]. Protective role of CKs on developing flowers exposed to HS was demonstrated [12]. Recently, CK induction of a high number of heat stress responsive proteins was reported in Arabidopsis [13].…”

Genetic diversity and population structure of rice landraces from Eastern and North Eastern States of India

“…Ahmadi and Fotokian [26] have indicated the linkage of markers RM251 and RM282 on rice chromosome 3 to potassium ion concertration. Lin et al ., [27] have shown linkage of RM112 and RM530 on chromosome 2 to leaf rolling in rice plants due to water stress. QTL mapping of rice indicated the linkage of rice grain and kernel length, breadth, length/breadth ratio kernel length after cooking and aroma to 18 different SSR markers [28,29].…”