Systems analysis of tapetal regulatory networks required for pollen development

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Pollen development is fundamental to plant fertilisation and seed formation, and is vital for the production of most of the food that we eat. It also plays a critical role in plant breeding and the production of hybrid plants. Hybrids (results of crossing two separate plant lines) tend to be more vigorous, with 20-30% higher yields, compared to self-fertilised lines. An example of how important this can be is seen with hybrid rice in China, where growing hybrid lines provides additional food for 60 million people/annum. However, the production of hybrids is both time-consuming and costly. We are becoming increasingly aware of population increases and the need for sustainable, effective agricultural systems, with increased yield but less environmental impact. Understanding the process of pollen formation is a vital step in such strategies since it provides an opportunity for selective breeding, maximising fertilization and hybrid production. Over recent years significant progress has been made towards understanding pollen development, much of this has come from studying mutants that fail to produce viable pollen (male steriles) in the model plant Arabidopsis. However recent advances, mean that information on pollen regulatory networks from Arabidopsis can now be applied to crops. We have shown that the pathways for pollen development between Arabidopsis and rice and barley are highly conserved; therefore such data can directly impact on strategies for crop breeding and hybrid production. One of the most important anther tissues for pollen production is the tapetum and many male sterile mutants show tapetal abnormalities. It plays a key secretory role in events associated with meiosis, pollen wall formation and in the development of microspores to pollen grains. However, little is known about the relationship between the tapetum and the developing pollen, although the tapetum has been shown to be essential. ABORTED MICROSPORE (AMS) is a key regulatory gene in the tapetum, which shows prolonged expressed during pollen development, which appears to have multiple roles during pollen formation, including early events associated with meiosis and later stages when synthesis and secretion of the pollen wall materials occurs. Our analysis of AMS during pollen wall formation has identified AMS regulated targets, including an ABC transporter, which is involved in the transport of pollen wall materials from the tapetum to the pollen and recently lipid biosynthesis for the pollen wall. However, it is also involved in earlier events, for example in the progression of meiosis and tapetal Programmed Cell Death. Although we have data that AMS regulates additional targets, there has been no characterisation of these other roles. In this proposal we want to build on our existing data and analyse the function of AMS throughout tapetal development. We will also analyse the expression of key components in the network using inducible AMS constructs and test them for their role in pollen development. We will use mathematical modelling of this pathway to help understand the cellular specificity of the network and determine components of the network, which are functioning in the communication between the tapetum and developing pollen. We will also determine how AMS regulates the expression of its targets and whether this is via a change in the status of the chromatin to make it accessible for expression. This work will provide a greater understanding of how the tapetum and the AMS regulatory network function to control pollen formation. It will provide valuable information about pollen development, which will be useful to facilitate control of fertility for breeding, and for the development of hybrid lines for increased yield. The regulatory networks found in Arabidopsis are conserved in the monocots rice and barley, thus the comparative analysis of these networks will directly impact onto crop research in the UK and worldwide.