Vol. 11, Special Issue 11 (2022)

Author(s):
Koppula Satya Sai Kumar, Shikha Jain, Ankit Raj, Sudheer Bishnoi, Pratik Prasad Singh, Eshwar Sai Prasad, Shikha Saini and Poonam Maurya

Abstract:
Heterosis has been widely exploited in plants and animals, and also revolutionized agriculture by improving important agronomic traits. However, the molecular mechanism is still remaining elusive. Circadian clocks are endogenous timers that enable plants to synchronize biological processes with daily and seasonal environmental conditions in order to allocate resources during the most beneficial times of day and year. The circadian clock integrates external signals such as temperature with internal temporal processes to generate robust rhythms. The circadian clock regulates a number of central plant activities, including growth, development, and reproduction, primarily through controlling a substantial proportion of transcriptional activity and protein function. Hybrids had higher growth and vigor under altered amplitude of expression peaks of circadian clock genes but maintaining the clock period. Down regulation of clock repressor genes, such as CCA1 during day time, up regulate the output pathways of photosynthesis and carbohydrate metabolism, which results in higher accumulation of chlorophylls, starch and sugars. Emerging insights into circadian clock regulation of fundamental plant processes, including responses to abiotic and biotic stresses, are discussed to highlight promising avenues for further crop improvement. Expression of some stress-responsive genes is induced in hybrids under stress conditions which helps in balancing the tradeoff between stress responses and heterosis. Hybrids generated from parents with greater expression differences in stress-responsive genes most often expressed higher vigor than parents with smaller expression differences. The evolving epigenetic and genomic field put forward the role of interaction of alleles from different parental genomes in reprogramming the genes involved in stress tolerance, fitness and growth of hybrids. The level of methylation of genomic DNA in hybrids was found to downregulate the circadian-regulated stress-responsive genes. Furthermore, epigenetic modifications of the circadian clock genes and their reciprocal regulators were reported to regulate the expression of downstream genes and pathways leading to more product accumulation in hybrids.